Polymers and the eco-design transformation. A cosmetic perspective

Since their description and characterization about a century ago, macromolecules have been highly valued for their unique properties and versatility. Natural polymers, such as rubber and polysaccharides, were among the first macromolecules to be used in commercial applications.1,2 However, despite their widespread use, the importance of the inherent properties of these macromolecules (e.g. repeating units, chain length, and molecular weight) was not immediately recognized.

Today, thanks to developments in chemical synthesis and petrochemistry, macromolecules with a variety of structures and properties have been developed, and polymers have become a versatile group of ‘materials’ that are used in diverse industries, for example, in the formulation of paints, tires, textiles, and cosmetics.3 In many of these applications, polymers are used to provide durable protection against the effects of daily use and aggressive environments and are the main, if not only, materials underpinning performance, but they can also be used as additives to provide beneficial properties.

Research into the development of polymers is a key field for cosmetic science. Indeed, polymers are present in almost all cosmetic formulations due to their wide range of intrinsic mechanical and phytochemical properties, such as their solubility (soluble or insoluble depending on the solvent), texture (sticky, soft, brittle, smooth, or rough), color (colored or uncolored), ability to self-assemble, biocompatibility, and biological activities.4 Polymers can, therefore, be used for a variety of cosmetic applications, including as gelling agents for water and organic solvents, as coating materials, and for their ability to stabilize emulsions or to disperse bulking agents (i.e. particles) in various media.

However, although the use of polymers has led to advances in the cosmetic industry and has enhanced the properties and performance of available products for consumers,5 most of the polymers currently used in cosmetic applications are petroleum-based and there is growing awareness of the ecological impact of these ingredients on the planet.6 The consequences of climate change, persistence of chemicals in the environment, and loss of biodiversity require a change in the way the cosmetics industry approaches product development. The future of innovation for the cosmetics sector, as for any industry, lies in a sustainable approach at every stage of the product life cycle, from design to end of life.

Sustainable innovation with a clear commitment to promote and develop eco-responsible technologies and environmentally friendly cosmetic products should be a fundamental goal for all cosmetics manufacturers, aligning the industry with the ten principles of the UN Global Compact.7 

Indeed, sustainable innovation will make it possible to respect the limits of our planet and the planetary boundaries defined in 2009 by an international team of 25 researchers led by J. Rockström of the Stockholm Resilience Center.8 A summary of the main impacts of human development on our planet is shown in Figure 1. To minimize these impacts, the cosmetics industry needs to be fully aware of these planetary boundaries and of the need to prioritize sustainable innovation through eco-design as far upstream as possible in the product development process.

Sustainable innovation requires strong and long-term commitments at all levels of organizations, and the development of scientific knowledge and tools to assess environmental and social impacts to allow the eco-design of new products and enable the different actors within organizations to speak the same language and participate jointly in sustainable innovation.

Adherence to the principles of green chemistry, first proposed by P.T. Anastas and J.C. Warner,9 is also essential for the development of environmentally friendly polymers. It is based on three fundamental pillars:

• Use of renewable raw materials,10 

• Development of eco-friendly processes,11 

• Innovation based on environmentally friendly ingredients.12 

These three pillars are indivisible if functional polymers are to comply with the principles of green chemistry: it is not enough to focus solely on using polymers of plant origin or to develop environmentally friendly processes, the research and development of new ingredients is also necessary.

In this review, we discuss the approaches that can be adopted by manufacturers and industry leaders to help meet the environmental requirements that are changing the cosmetics industry, and describe some of the tools and methods that have been established to assist the implementation and monitoring of all three of the pillars of green chemistry during cosmetic product development and production. The contributions of numerical and computational methods, as well as the lessons to be learned from bioinspiration to achieve the desired transformation of ingredients, are also described. We then provide a summary of the main properties and uses of existing polymers in cosmetic formulations, and highlight the challenges associated with replacing these ingredients with equally performant, safe, sustainable, and environmentally friendly alternatives. Finally, we describe the most promising families of polymers that we believe will be central to the cosmetics industry in the coming years.

Applying the principles of green chemistry to the development and production of cosmetic products requires three main commitments: 1) to meet the first green chemistry pillar of using renewable materials, manufacturers should aim to constantly increase the volume of polymers of renewable origin used in their marketed formulations; 2) to achieve the second pillar of developing eco-friendly processes, manufacturers need to identify synthetic processes with the lowest possible environmental impact and then promote and expand their use to marketed products; and 3) to apply the third pillar of environmentally friendly innovation, biodegradable and low-footprint polymers should be developed and integrated into marketed formulations to limit the impact of existing products on the environment, particularly the aquatic compartment, at the end of the product’s life cycle after use by consumers.13 

Meeting the objective of sustainable sourcing requires industry to consider the renewable plant origin and sustainability of the raw materials used for polymer synthesis during the eco-design of functional polymers, before any development work in the laboratory takes place. To this end, all data necessary for validating that source materials respect all aspects of nature and biodiversity conservation, including culture media for fermentation reactions, should be provided by suppliers for all stages of plant extraction and processing. In addition, the use of byproducts from other plant-based processes (e.g. those used in the agro-food industry) should be preferred.

Measurement tools, such as the ¹⁴C carbon analysis method,14 to validate the renewable origin of raw materials must be used when in doubt or when mixing raw materials. This test method distinguishes between carbon in a product that is derived from contemporary carbon inputs and that derived from fossil-based inputs. A study demonstrating that the tracing and quantification of renewable compounds by their intrinsic ¹⁴C content could be applied to cosmetic ingredients was published 2019.15 Indeed, in this study, 216 carbon-based cosmetic ingredients with different properties and structures were evaluated using this promising analytical technique, validating its key contribution for assessing the natural origin of ingredients.

The identification and development of sustainable pathways and processes for the synthesis of eco-responsible polymers is based on metrics specific to the principles of green chemistry, such as atom-saving calculations, which help maximize the incorporation of atoms in the starting materials into the final molecule, or use of the E-factor16 to evaluate the mass of waste generated by the process. This latter measure is particularly important, as it can be assessed during the early eco-design phase and subsequently reassessed during the industrial stage to allow the quantity of solvents and process-related waste to be minimized.

Tools for assessing the ‘naturalness’ of materials and processes are also key for validating compliance with the first two green chemistry pillars, namely, renewable sourcing and the development of processes for the synthesis of polymers consistent with the principles of green chemistry. The combination of these two indices can be evaluated using the ‘naturality index’, according to the detailed methodology described by Philippe et al.,17 and in line with international standard ISO 16128-1,18 which provides guidelines on definitions and criteria for natural and organic cosmetic ingredients and products.

In addition to applying the principles of green chemistry to the development of new polymers for innovative cosmetic formulations, it is essential to consider their impact on the environment after consumer use, in the same way as for other ingredients. After use, cosmetic products are often washed down the drain and end up in the aquatic environment.

Major steps toward reducing the environmental impact of cosmetic products can be achieved by focusing on two easily manageable eco-design levers: biodegradability and the gray water footprint (Figure 2).13 

Biodegradability is the ability of organic ingredients in the formula to be rapidly and completely degraded by microorganisms in the environment. To follow an eco-design approach to formulas, an ingredient should be considered biodegradable if it is found to be ‘readily biodegradable’ in a test conducted in accordance with an OECD guideline (test 301,19 test 310,20 or equivalent). This ‘readily biodegradable’ status can also be obtained by analogy with an ingredient of similar chemical structure.

Numerous experimental tools and methods have been developed to study the (bio)degradation of polymers in a controlled or standardized environment.21–24 International standardization institutes have developed standard test methods to confirm the biodegradability or compostability of materials. In this context, biodegradable plastics must meet stringent standards with respect to ultimate biodegradability, compost quality, and product safety. In addition, some studies in the scientific literature show how laboratory-scale methods can be used to better predict environmental biodegradation.25 

However, polymer (bio)degradation in managed and unmanaged environments is not universally well understood:26,27 the (bio)degradation pattern of a polymer-based material depends on many factors such as its crystallinity, its density, the presence of additives, and the environment (e.g. presence and diversity of competent microorganisms, temperature, moisture, and pH), making it difficult to measure (bio)degradability in a generic way. Indeed, the Committee for Risk Assessment (RAC) of the European Chemicals Agency (ECHA) has pointed out the lack of nontesting methods to predict the biodegradability of polymers.28 

Compared to smaller molecules, polymer (bio)degradation is more material-specific and complex.29 This specificity and complexity must be addressed to build a relevant and robust tool for predicting the (bio)degradability of polymers, while also taking into account potential degradation, whether physical (induced by heat, irradiation, etc.), chemical (induced by the presence of specific acids, bases or oxidizing agents, etc.), hydrolytic, or biological (induced by the presence of specific microorganisms). Furthermore, the timeframe of (bio)degradation (primary, ultimate) and the nature and quantity of the resulting degradation products, as well as their fate, must also be considered.

In cosmetics and many other industries, combining high biodegradability and adequate functional efficiency is one of the major challenges for the field of eco-designed polymer formulas.

Nonpersistence in the environment is becoming another characteristic of interest for ingredients and particularly for polymers. The nonpersistence of a given chemical reflects its capacity to be fully degraded by physicochemical and/or biodegradation processes within a time scale that ensures no accumulation or remanence of the parent compound, and of any by-products, in the environment. Criteria and methodologies for assessing the persistency of chemicals are detailed in technical guidelines provided as annexes to chemical regulations, such as those provided in Europe by the ECHA and in the USA by the United States Environmental Protection Agency.30–32 

The gray water footprint is derived from methods used to calculate the critical dilution volume of an ingredient or formula, one of the key criteria considered in awarding the European Eco-label to cosmetics.33,34 This footprint is defined as the theoretical volume of natural fresh water required to dilute an ingredient or cosmetic formula to a concentration with no foreseeable toxic effects on aquatic species (i.e. no aquatic toxicity) after consumer use of the product (Figure 2).

It relies on key environmental characteristics to determine the impact of ingredients released into drains: the potential for biodegradability in the environment and toxicity to aquatic species. For the eco-design of cosmetic products and as a general rule, a footprint of less than 10⁵ per g can be considered favorable.13 

Efforts are also being made to develop methods to quantify the global environmental and social impact of cosmetic products. One example is the SPOT (Sustainable Product Optimization Tool) methodology, which is based on a life cycle assessment of finished products. SPOT applies the concepts of normalization and planetary boundaries to weigh and aggregate the various impacts of a product throughout its life cycle, resulting in a single environmental footprint35. This type of methodology and the knowledge gained from such life cycle assessments can be used as eco-design tools by product development teams to improve the environmental and social profile of new products.

Cosmetic product development generally follows an iterative process, starting from ideas or consumer-centric needs and expectations, and progressing through stages of knowledge gathering, multi-expertise characterization, design of experiments, and proof of concept. However, this process is very laborious and time-consuming, monopolizes resources, and is not fully adapted to new technical advances and consumer needs (fast time-to-market, personalization, highly specific functionalities with trusted ingredients, etc.). In many other fields, extensive use of computer-aided modeling is fully integrated into classical engineering and experimental processes. Such approaches have already been applied to enable the property targeted design of synthetic polymers and bioplastics, and to facilitate chemical deformulation36–38 and are clearly relevant to cosmetic scientists, particularly for advancing the development of new products that meet green chemistry standards and contain sustainable ingredients. Most notably, digital tools can be useful for providing valuable insights into the potential impact on product performance of substituting current ingredients with new or existing greener alternatives, and could eventually be used to predict the environmental performance of product components, including polymers.

Today, much effort is focused on making cosmetic products increasingly natural by substituting historical petrochemical-based ingredients such as polymers with naturally derived alternatives such as polysaccharides, without sacrificing performance. However, due to the complexity of most of the formulations, solutions, emulsions, and other mixtures of components used in the cosmetics industry, the development of new safe and biodegradable products is a particularly challenging task.39 Indeed, these formulations are often multiphase systems and their properties are highly sensitive to the substitution/addition of new compounds. In addition, most of the inherent mechanisms involved in maintaining the properties of these systems under given conditions remain poorly understood.

Replacement within a formulation of one or more ingredients that are known to be effective from the consumer’s point of view first requires a preliminary phase that can be divided into several steps: in vitro–in vivo correlations to define performance, translation of performance into scientific levers and their identification, and deconvolution of the levers into modes of action. This first phase is a top-down process that aims to understand how an empirical formula works, allowing the identification of the key mechanisms of action of the active ingredient, with the aim of substituting some components of the formula while ensuring that the performance phase is not disturbed. It should be emphasized that this top-down phase may comprise many intermediate steps, depending on the complexity of the product, and may require considerable resources. Digital assistants, such as modeling assistants, can provide useful toolboxes for each of the above top-down steps, from statistical analysis frameworks to multiscale modelling.40–42 Once the salient features that drive performance have been identified, a second phase emerges, often in the form of an iterative loop: proposing an identikit model with new natural ingredients that are as close as possible to the targeted descriptors. Digital approaches are at the heart of the innovation process and have been used, for example, to replace anti-dandruff agents in cosmetic shampoos with more environmentally friendly compounds.43,44 Many digital approaches have recently been developed to facilitate this iterative innovation loop, ranging from classical mechanistic methods (see Luengo et al.³⁹ for an overview and their applications in polymer-containing formulations) to data analytics and data-driven methods.

Although this ‘isoperformance’ approach to substituting formula ingredients may indeed be a way of innovating toward green and sustainable products, it assumes that the preliminary phase discussed above can be carried out. This prerequisite phase is often a complex, deconvoluted, and time-consuming process, which usually relies on substituting base formula components with natural ingredients that lack specific requisite features, resulting in problems such as solubility issues or incompatibility with other ingredients. Alternatively, green science innovation could be accelerated by taking a different route, such as rethinking formula spaces, performance spaces, and chemical spaces. These three pillars of innovation are extremely difficult to manage within industrial frameworks and infrastructures, which need to quickly deliver safe products under time and market constraints.45 The challenge is therefore to develop and use digital tools that bridge all scales, from molecular structures, macromolecular assemblies, and formulations, through to experimental design and performance prediction. These tools place data at the heart of the innovation process, but also allow for hybrid strategies involving the mechanism-based approaches described above and experimental techniques. The strategy is therefore to address ingredient substitution to achieve greener formulations, while exploring new formulation and performance options.

Developments in data-driven science and hybrid methods have been achieved in recent years, most notably in cases where the relationships between inputs (structures and molecular descriptors,46–48 physicochemical and other parameters,49–52 and compositions and phase diagrams53–56) and outputs (functional performance, in vitro performance, sensorial performance, etc.57–59) exist but are unknown or unclear. The initial development of such methods required large amounts of data, but recent implementations have used low-data regimes,60,61 with success being achieved through active learning methods.62–64 For example, the emergence of data-driven approaches in the fields of hard matter65 and soft matter science66–68 has enabled the discovery of new materials with targeted properties and new functional properties. It has even become possible to retro-design polymeric69–71 and small-molecule72 materials starting from user-defined properties. The application of data-driven methods makes even more sense when knowledge, expertise, or mechanistic information is introduced into the loop, so that problem-driven methods can be combined with the learning stage, either through data augmentation (and vector representation of descriptors within featured spaces) or through enrichment of additional physical, chemical, or mathematical models. The concept is thus to couple structure–property machine-learning models with a subspace of material species for which these models can associate the properties of the materials with a set of descriptors that will augment the features in the data-driven model. The machine-learning approach will thus be capable of inferring the structures of the materials or the composition of formulas from the descriptors and ensuring that the macromolecules present in the formula meet the prerequisite standards of naturality or green chemistry. Active-learning methods can also help to feed the model by performing biodegradability tests on the resulting candidate materials.

Prediction of chemical environmental endpoints through modeling using (Q)SAR tools is today common practice for small molecules entering application domain of these models. These tools can be used for screening purposes, and are increasingly being deployed to provide evidence of characteristics, such as ready biodegradability or low bioaccumulation potential, which are required by regulatory frameworks (e.g. the REACH regulation in Europe), and are described in guidance documents providing information on the generation and reporting of such data.73 In other words, (Q)SAR results regarding environmental properties are now well accepted by regulatory authorities as an alternative to test results for hazard and risk analysis of small chemical molecules.

However, to date, no publicly available model has been developed for predicting the environmental endpoints of larger molecules such as polymers.

Nature constitutes an inexhaustible source of sustainable innovation. The biomimetic approach is therefore crucial for the eco-design of innovative polymers.74,75 Indeed, the inherent biodegradability and recyclability of natural molecules make bio-inspiration a decisive factor in achieving both innovation and respect for the planet, allowing problems such as chronic ecotoxicity to be avoided or limited.

For nearly 50 years, there have been many initiatives to promote and support the development of this approach, such as the Biomimicry Institute,76 with its description of original materials in nature,77 the European Centre of Excellence in Biomimicry,78 and the Biomimicry 3.8 platform.79 

Similarly, the development of toolboxes for biomimicry in eco-design is a valuable aid to achieving the development of innovative and sustainable ingredients,80–83 such as polymers, thanks to a framework of ten principles that must be considered before any industrial development begins:

1. Nature uses only the energy it needs and relies on freely available energy.

2. Nature recycles everything.

3. Nature is resilient to disturbances.

4. Nature optimizes rather than maximizes.

5. Nature rewards cooperation.

6. Nature runs on information.

7. Nature uses chemistry and materials that are safe for living beings.

8. Nature builds with abundant resources and uses rare resources sparingly.

9. Nature is locally attuned and responsive.

10. Nature fits form to function.

These principles align fully with those established during the development of green chemistry. Naturally, they are also fully in line with the aim of sustainable development, and take account of biodiversity, resource management, and the concept of environmental and social responsibility.

The relevance of this approach is reinforced by an international definition of the terminology used in the field, set out in ISO 18458:2015, Biomimetics – Terminology, concepts and methodology, which was revised in 2021.84 

The use of an eco-design approach based on biomimicry, and complemented by the principles of green chemistry, is thus a preventive process designed to anticipate the major health and environmental impacts of the sourcing and manufacturing of polymers, including synthetic pathways and processes, throughout their entire life cycle.

In nature, enzymes are the catalytic tools used to generate and transform renewable organic materials. Enzymes allow regional and stereo-specific modifications, as well as the biodegradation and recycling of materials, all of which are processes central to understanding and supporting eco-design.

Thus, the biomimetic approach examines the specifications of life to understand its characteristics, how materials interact, how they are composed, and how they evolve.

Imitating the remarkable properties of materials and systems obtained via natural chemistry is therefore fundamental for the design of innovative new polymers, especially for identifying ingredients for use in various skin and hair cosmetic products.

A very good example of the high value of this approach in cosmetics is the great success of hyaluronic acid, a disaccharide polymer composed of d-glucuronic acid and N-acetyl-d-glucosamine linked by alternating β-(1→4) and β-(1→3) glycosidic bonds (Figure 3).

This natural polymer is widely distributed in human tissues, most notably in the epidermis, and as a component of the extracellular matrix of basal keratinocytes, it provides critical functions such as mechanical, lubricating, and hydrating properties.

Use of the biomimetic approach, which led to the identification of the unique structure–activity relationships of this polymer,85 combined with the derivation of bio-inspired industrial processes from biotechnological processes,86 has enabled the successful sustainable innovation of hyaluronic acid in cosmetics.

Despite increasing recognition of the need to improve sustainability and reduce the environmental impact of cosmetics and ongoing efforts into the research and development of more sustainable alternatives (discussed in Section 4), many different petrochemical polymers are still widely used as ingredients in haircare, skincare, and personal care products (e.g. hair shampoos and conditioners, skin creams, gels and serums, and makeup products) in which they function as key conditioning, rheology-modifying, film-forming, emulsifying, and filling agents (reviewed in detail by Loh,87 Lochhead et al.,5 Alves et al.,88 Gawade et al.,89 and Philippe et al.90).

Replacing the petrochemical polymers currently used in cosmetic formulations with naturally occurring and biodegradable macromolecules is challenging.91 First, eco-friendly polymers need to at least display the same functional properties as the polymers currently used in cosmetic applications and be capable of retaining their functionality for a period corresponding to the lifespan of the product or until the end of its use. Second, petrochemical polymers have the advantage of being relatively easy to design and physiochemical studies have allowed precise relationships to be established between the homogeneous structures and relatively constant composition of these macromolecules and desired properties.4 Third, evaluating the biodegradability of polymers is a complex process: as described in Section 2.1 polymer degradation is influenced by numerous external (e.g. environmental) and internal (e.g. intrinsic structural characteristics) factors, and the mechanisms involved in the degradation of macromolecular chains are often complex and, in some cases, remain poorly defined in natural environments.26,27,92 Thus, extensive research and development are needed to study the structure–function relationships of new eco-friendly polymers, thoroughly assess their biodegradability, and to optimize the functional properties of these ingredients when incorporated into the wide range of systems used for cosmetic applications. In addition, switching entirely to the use of sustainable alternatives will likely require industry to adapt or make concessions for factors such as the greater structural variability of naturally occurring macromolecules. To highlight the challenges faced by the cosmetics industry as it undergoes the transition to sustainable innovation and adopting green chemistry approaches, a summary of the main desired properties and types and families of existing polymers used in cosmetic applications is provided below.

The functional properties, structure–function relationships, and behavior and performance of polymers in the media or carriers in which they are contained are dependent on several key physiochemical and mechanical characteristics (summarized below).

The behavior of polymers is strongly influenced by the distribution of molar masses, as well as by the molecular structure of the monomer units and the way in which they are linked together. A good knowledge of the structure of polymers is a prerequisite for establishing good structure–property relationships. Naturally occurring polymers do not always have reproducible structures due to their natural origin and the influence of season. In general, high polydispersity is observed and complex structures, often branched (i.e. polysaccharides), have been demonstrated.91 Furthermore, when used in cosmetic applications, these polymers may be dispersed in a solvent, forming aggregates that require appropriate characterization. A range of methods can be adapted to characterize the structure of polymers, including size exclusion chromatography, electrophoresis, dynamic light scattering, and NMR. In the field of polysaccharides, field-flow fractionation is a very common separation and characterization technique.

These methods have already been used to extensively characterize, and assist in the design of, the polymers currently used in cosmetics, which present many different structures. Homopolymers are the most common structures, but block copolymers can also be used. For example, the block copolymers (triblocks and diblocks) made by Kraton Corporation consist of an elastomeric block in the middle and a rigid thermoplastic polystyrene block at the end of each polymer chain (Figure 4). These copolymers containing polystyrene and synthetic rubbers, such as isoprene or butadiene midblocks, provide both elasticity and a thickening effect and are used as rheology modifiers and film-forming agents in skincare, haircare, and makeup products.93 

A further example of the application of block copolymer synthesis for use in cosmetics is the generation of polyacrylate triblock copolymers (e.g. 2-ethylhexyl acrylate and methyl acrylate; P2EHA-b-PMA).94–96 In this case, the block copolymers are synthesized by reversible addition-fragmentation chain transfer (RAFT), a well-known controlled polymerization technique that allows the generation of well-defined structures.94–96 This RAFT approach, used simultaneously with self-assembly, leads to the generation of polyacrylate particle dispersions with low polydispersity that remain stable in organic media and can therefore be used in film-forming makeup products.95 

Thermal properties – such as the glass transition (T_g), crystallization, and melting temperatures of polymers – can also be important in determining the functional characteristics of polymers. For example, these properties impact the duration of wear of nail varnishes and the mechanical stability of lipsticks in different climatic conditions.

Several parameters can influence the thermal properties polymers, such as the structure of the constituent units of the polymer and their sequence, branching, polydispersity, and interactions with solvents. The method of assessing thermal properties must be adapted (calorimetry, rheometry, etc.), depending on the physical state of the polymer (powder, dispersion, or solid). In the case of cosmetic film formation by evaporation of water, parameters such as drying kinetics and final T_g may differ depending on the water content of the film. Therefore, thermogravimetric drying curves must always be recorded under the same conditions.

In cosmetics, T_g temperature has an impact on the thermal stability of formulations containing dispersions of polymers, as well as on application phenomena such as ease of spreading and durability. An example of how higher T_g temperatures impact the durability of dried films of nonaqueous dispersions (NADs) is shown in Figure 5. In this example, films of NADs of block copolymers (isobornyl, methyl, ethyl acrylate, and acrylic acid), formulated in the cosmetic emollient isododecane as would be used for lipstick or foundation applications, were applied to a skin-model substrate.97 The three NADs tested differed in the weight percentages of the various monomers, with NAD-3 having the lowest methyl acrylate content (10% of polymer) and NAD-1 having the highest content (80% of polymer). Films formed from NADs with >50% methyl acrylate, such as NAD-1, have a higher T_g. As a result, they are less cohesive and fragment easily when the substrate is stretched (Figure 5).

The final state of the polymer (film, particle, etc.) can confer highly optimized mechanical properties to cosmetic formulations, including the final shape and brittleness or rigidity of a material. For example, in mascara, the rigid properties of the natural polysaccharide sodium alginate (INCI name: algin) can be used to confer tensile properties on to the eyelashes and induce curling (as shown in Figure 6).

The viscoelastic behavior of the polymer is generally the fundamental factor that must be optimized: Young’s modulus and dissipation control not only mechanical strength but also durability. In fact, the durability of cosmetic coatings is linked to their resistance to various mechanical stresses. Depending on the application, varying levels of deformation may be required. The presence of a degree of elasticity can ensure better durability of the cosmetic effect. Mechanical property tests are conventionally carried out in traction/compression, but they also include thermodynamic analyses through dynamic mechanical analysis.

Polymeric films are fundamental components of cosmetic formulations. Although commonly used in cosmetics, the physical chemistry of film formation by evaporation of a solvent is complex and far from being fully understood, even for widely used petrochemical polymers. Films must present certain functionalities, such as protection, filling in wrinkles, maintaining the pigments present in coatings and so on. In all cases, polymer films must adhere well to the target surface (e.g. hair, skin, nails). For some applications, such as in makeup formulations, polymer films must also be easily removable. Good control of these properties is very important in the quest for cosmetic product performance. In general, the structure of the polymer is crucial, and it is thus necessary to control factors such as microscopic organization and surface roughness. Wettability and peeling tests, as well as observation by light or electron microscopy, are all tools that help provide a better understanding of these properties.98Figure 7 shows how these techniques can be applied to study polymer behavior during drying and after film application. For example, light microscopy can be used to show how rapid drying of aqueous dispersions can lead to internal stresses and curling (Figure 7(a)). Microscopy also shows how polymer particles coalesce during the drying of aqueous dispersions and how the degree of coalescence influences optical properties (Figures 7(b) and 7(c)). Finally, scanning electron microscopy can be used to study polymer films applied to target surfaces to evaluate factors that may impact product performance such as heterogeneity (Figure 7(d)).

The adhesive properties of coatings can be evaluated using various methods, such as the peel test99,100 or the cross-cut test.101 The latter is a common test that has been adapted following its use in the paint industry. The test consists of applying a dry coating on a substrate and then making a cross-cut pattern using a standardized ‘cross-cut’ tool. Adhesive tape is then applied and forcefully removed. The number of cross-cut squares removed by the tape is then checked to evaluate the adhesion of the coating. The cross-cut test is particularly useful for nail polish applications, such as evaluating the impact of moisture exposure on nail polish adhesion (illustrated in Figure 8).

The test is simple to perform and provides a rapid quantitative assessment of the adhesive character of any coating. Indeed, research teams have also used this test for foundation applications.102 This test is standardized by ASTM D3002-07, ASTM D 3359-09e2, and ISO 2409:2013 and therefore provides a valuable to tool for testing the impact of new ingredients on the performance of cosmetic products.

Functional properties: Polymers also play an important role in enhancing the sensory attributes of cosmetic products, such as the tactile characteristics of formulations before application, and the feel of the skin or hair during and after application. For example, the adhesive or lubricating properties of cosmetic products are highly dependent on the rheological characteristics of the polymers dispersed in the formulations, as well as on the changes in the structure and properties of the coating that occur during evaporation of solvents and on the formation and smoothness of deposits, which affect tactile perception on touching.

For hair applications, the eco-design of alternatives to classic ingredients, such as substitutes for ecotoxic synthetic cationic polymers, must be based on the evaluation of friction properties, which are directly related to the tactile properties of formulations and their detangling capacity. Several studies39,103 have been conducted to gain a greater understanding of the factors that influence polymer film formation, structure, and thickness, and more specifically the arrangement of the macromolecular chains on the surface of the hair during shampooing. Overall, these studies showed that the relative amount of positively charged monomers was a determining factor for film thickness, along with concentration and ionic strength. These findings have important implications for the use of natural polymers in hair applications: in the case of a polymer of natural origin such as chitosan, these charge densities are lower than those exhibited by quaternary cationic polymers of fossil origin such as poly(diallyldimethylammonium) chloride (polyDADMAC), implying that chitosan would be more difficult to neutralize and precipitate in the presence of anionic surfactants and thus would less readily form the large deposits and thicker films needed for good cosmetic performance.

Testing of sensory and tribiological properties: The thickness and water content (water fraction: Xw) of adsorbed polymer films can be determined using two techniques: quartz crystal microbalance (QCM) and ellipsometry. These techniques have already been used to evaluate and compare the properties of chitosan and polyDADMAC deposits (as illustrated in Figure 9). The results revealed clear differences in the hydrated and nonhydrated thickness of chitosan deposits after rinsing in the presence of an anionic surfactant (sodium lauryl ether sulfate), whereas the values for polyDADMAC remained relatively constant. The derived water fraction value for chitosan was therefore much higher than that for polyDADMAC, impacting the capacity of chitosan to form thick films after application. Indeed, the observed differences in these parameters correlate with cosmetic performance, as measured in in vivo studies assessing the feel and untangling of hair fibers (as described by Hernández-Rivas et al.).104 

Polymers are widely used in cosmetics to modify the rheology of formulations. Rheological control is important for facilitating the application of cosmetic formulations onto target surfaces or substrates, and for improving product shelf-life (e.g. limiting the sedimentation and phase separation of ingredients). For example, a liquid foundation must be sufficiently robust to allow the suspension of pigments to be maintained under storage conditions, while also enabling adequate flow and viscosity during use. Rheology-modifying polymers are also important for consumer perception as they make it possible to design formulations with the desired texture (viscosity, flow, etc.), and thus these polymers play a major role in sensory perception during the use and application of products by consumers. Both natural and synthetic polymers are used as cosmetic thickening agents.

In skin and hair care products, crosslinked polyacrylic acid (INCI name: carbomer) is the classic polymer used in water-based systems. Carbomers are a family of cross-linked acrylic acid polymers105 that can be thickened by charge-induced chain extension, chain entanglement, and hydration. The viscosity of these polymers is low at acidic pHs, but increases when the acid groups are neutralized with alkali or organic amines (see Figure 10). They therefore form microgels capable of swelling in water and are currently used to build viscosity and suspend oil droplets or particles. Although not eco-designed, carbomers are still widely used in cosmetic formulations and combine affordability, efficacy at low concentrations, and good sensorial effects at the same time.

Another top-performing family in this category is a copolymer containing the acrylamido-2-methylpropanesulfonic acid (AMPS) monomer. These copolymers are typically obtained by radical polymerization (see Figure 11) using a process that begins with the decomposition of an initiator, such as ammonium persulfate or azobisisobutyronitrile (AIBN), into free radicals. This can be achieved through thermal decomposition or redox reactions. AMPS is often combined with other monomers like acrylamide (AM) or sodium acrylate (NaA) using a copolymerization process that involves the simultaneous polymerization of these different monomers, resulting in copolymers with properties derived from each monomer. The resulting copolymers are highly cross-linked and pre-neutralized), which means they are very efficient at low concentrations and, unlike classic carbomers, they do not require neutralization to be efficient. The grade of AMPS incorporated can be varied depending on the required function, leading to the generation of copolymers that perform better than conventional carbomers under certain conditions (e.g. at an extreme pH, or in the presence of electrolytes, or surfactants). These beneficial properties are due to the pKa of the SO3H group being lower than that of –COOH.

As another alternative to carbomer, and with the aim of generating skincare products that form a perfectly homogeneous film on the skin, a new polymer has been developed, termed Netlock^TM technology,107,108 based on the use of a polyacrylate copolymer, INCI name: C12–22 alkyl acrylate/hydroxyethyl acrylate. This semi-crystalline polymer forms a gel and stabilizes droplets containing UV filters, creating an extremely dense and protective structure. The filters are therefore anchored in an ultrathin film that is invisible on the skin, giving formulations greater efficacy and resistance to water, sweat, and sand, while preventing product migration into the eyes.107,108 However, although this polymer is non-ecotoxic and the technology enhances properties such as the durability and resistance of sunscreen formulations, and thus helps to limit migration into the environment, the polymer was not developed through eco-design and in terms of life cycle assessments is not biodegradable.

Thus, although these modifications and innovations have improved the functional properties of polyacrylates, there is still space for improvement in terms of the sustainability of carbomers and their derivatives. Currently, the monomers used to make these polymers and copolymers are still derived from petrochemicals. Research is ongoing to look for bio-based monomers that are sustainably sourced. In addition, not all the reactions involved in the process of generating carbomers and their copolymers follow green chemistry principles: efforts are underway to develop a more environmentally friendly method of making polyacrylate polymers. In particular, research is ongoing into the potential of using polyacrylates based on bio-renewable sources, such as lignocellulose, alongside the development of greener synthetic processes.109 In addition, while the ecotoxicity profile of carbomers and carbomer-derivatives is good, most of these polymers are not biodegradable, resulting in a sub-optimal end-of-life profile. As discussed in Section 4, the main strategy for replacing the widespread use of carbomers in cosmetics is the use of polysaccharide polymers. A wide variety of modified natural polymers with extremely interesting sustainability potential are now available on the market. In particular, naturally occurring polysaccharide polymers (e.g. xanthan gums, celluloses, starches, and gums) have been extensively characterized as raw material substitutes for synthetic rheology-modifying polymers and are widely used in cosmetic formulas (see Section 4), as well as in other industries.110 However, further developments are needed to improve the rheology and sensory-modifying properties of these naturally occurring polymers and ensure that products containing these ingredients achieve the desired level of performance.111 

Finally, polymers can also be used to stabilize Pickering emulsions. This feature avoids the use of surfactants which can adversely affect the properties of the final formulation.112–115 The main challenge regarding the use of Pickering emulsions continues to be the stability of the final formulation.

Particulate polymers can impart optical properties that are highly valued in creams. However, in makeup, the addition of these polymers can impart a sticky feel, which is not desired by consumers.5 These properties can be measured using in vitro tribological tests.

Fillers composed of polymers such as polyamide (nylon) or poly(methyl methacrylate) (PMMA) are classically used in facial applications, such as foundations, to absorb sebum and enhance matting effects. However, studies have shown that cellulose particles have better sebum adsorption properties than particles of these synthetic polymers and that by switching from native cellulose to microparticulate forms, the particles derived from this natural polymer are able to rival the performance of petrochemical particles, especially regarding the matting effect.116,117 Indeed, cellulose microparticles have already been introduced in some brands (e.g. L’Oréal Paris™ Infallible 24H range containing the cellulose filler TEGO^® Feel C 10).117,118 

As noted above, the different types of polymers most commonly used in cosmetics have already been described in detail in the literature (see Loh,87 Lochhead et al.,5 Alves et al.,88 Gawade et al.,89 Philippe et al.90). In this section, we provide some examples of polymers commonly used in cosmetics for specific applications, including hair conditioning polymers, rheology modifiers, film formers, emulsifier polymers, and fillers. These existing polymers present high performance and fulfill specific functions in cosmetic formulations, illustrating the challenge of replacing existing polymers with sustainable and environmentally friendly alternatives. However, they also often face some sustainability issues, and thus current trends toward more sustainable solutions are also described.

For consumers, hair conditioning properties can be defined by two main perceived benefits on both wet and dry hair: fiber lubrication during combing and the feel of the hair. The complexities and challenges of developing sustainable shampoo and conditioner ingredients and formulations to meet current and future needs have been recently reviewed in detail.119 

Today, several environmentally friendly shampoos and conditioners (e.g. products containing non-ecotoxic and biodegradable ingredients) are commercially available. However, these formulations do not offer the same level of performance as the most widely used products containing nonsustainable ingredients. There is currently no way of achieving this level of performance other than with cationic polymers and silicones.

Polyquaternium-10 is the most widely used hair conditioning polymer in shampoo formulations today. As explained by Patil et al.,4 due to its high charge density, polyquaternium-10 has a good affinity for hair fiber and, when used alone, shows good performance in reducing friction on wet hair. However, its performance is further improved by coacervation, a very well-known physicochemical method that consists of mixing anionic surfactants, cationic polymers, and silicones. Lochhead used this method to deposit a thin film of silicone on hair fiber.5 The main silicones used for this application are dimethicone and amodimethicone.

There are two major sustainability challenges with this type of polymer. First, the process of quaternizing the amine groups involves the use of toxic reagents and solvents and thus is not an environmentally friendly reaction. Second, the end-of-life profile of these raw materials needs to be improved in terms of the pillars of ecotoxicity and biodegradability. Most of these polymers are highly ecotoxic due to their cationic charge and they are not biodegradable. At present, the main alternative to using polyquaternium-10 in hair conditioning products is to substitute this petrochemical polymer with a cationic guar (INCI name: guar hydroxypropyltrimonium chloride); however, as discussed below (Section 4), these bio-based polymers still need to undergo the quaternization process and therefore cannot be considered as a truly environmentally friendly alternative.

In the cosmetics industry, film-forming polymers are used in a wide range of applications such as sun protection, semi-permanent hair coloring, makeup, and styling products. The main challenge for cosmetic formulators remains the durability of these products after application. In order for a product to be long-lasting, polymers in the formulation must adhere to the skin and be resistant to water and lipids (e.g. sebum, and oils from food, such as olive oil). Currently, silicones are the only cosmetic ingredients available that can meet both challenges: they are easy to formulate, have good mechanical properties, good stability on substrates, and are resistant to water and oils. Since the 1990s, the main technical approach to achieving long-lasting makeup has involved using combinations of silicone resins with monofunctional and quadrifunctional silane functional groups (MQ resins) (Figure 12) and a plasticizer.

MQ resins are mesoporous and their pore size corresponds to the size of the functional groups. They allow pigments to adhere to skin but have the disadvantage of causing stickiness and discomfort and therefore need to be plasticized with substances such as volatile oils, volatile silicones, or hybrid silicone copolymers. The formulator’s task is to find the perfect balance between the MQ resin and the plasticizer to achieve a good compromise between adhesion and comfort.

Several issues have been raised regarding the widespread use of silicones; however, these concerns have not always been based on solid science.9 The real challenge surrounding the use of silicones in cosmetics is their end-of-life profile, as like most polymers, silicones are not biodegradable.

Although technologies based on hydrocarbon polymers have been developed to find alternatives to silicones, the main challenge continues to be ease of formulation in oil or water, while maintaining resistance to these same media once the film is formed on the substrate (skin, hair, etc.). To overcome this challenge, polymers dispersed in volatile oils (nonaqueous dispersion technology) have been developed using acrylate chemistry. This strategy involves a two-step dispersion polymerization process based on methacrylate121 (Figure 13).

Radical polymerization then allows the production of a tailored polymer structure that provides the required properties, including adhesion. Compared to the generation of silicone polymers, acrylate chemistry is a more versatile strategy that allows easy modification of polymer properties and, particularly in the case of isobornyl acrylate, makes it possible to introduce a carbon backbone from renewable sources. Although these polymers are non-ecotoxic, the main negative point of this family is related to the end-of-life profile of NADs of this polymer, and specifically the issue of biodegradability.

Most cosmetic formulations consist of oil-in-water emulsions (used in most skin care products) and water-in-oil emulsions (currently used in makeup formulations, particularly in foundations).

Today some very interesting nonpolymeric hydrophilic emulsifying agents have been developed to stabilize oil-in-water emulsions, such as alkyl polyglycosides (INCI names: caprylyl/capryl glucoside), which combine an eco-designed profile (bio-based, green manufacturing, and favorable end of life), excellent stability, and good sensory properties.

Unfortunately, for water-in-oil emulsions, the choice of eco-conceived emulsifiers is much more limited. It is very difficult to find good candidates that combine the three essential factors stated above. To stabilize emulsions, some amphiphilic polymers are needed to protect the interfaces from destabilization (coalescence and Oswald ripening). Consequently, most foundation formulations consisting of water-in-oil emulsions are stabilized with hybrid polyethylene glycol-silicone polymers (such as the example shown in Figure 14).

This kind of polymer presents two main challenges: the ethoxylation reaction, which is very far removed from the principles of green chemistry, and the poor end-of-life profile associated with silicone.

Polymeric fillers play a central role in consumer’s immediate perception of efficacy, especially in skin care and makeup. In fact, these particles are added to formulations to enhance sebum absorption and blur imperfections, and to improve the feel of the skin during and after application.

For some years now, the quantity and variety of natural fillers have been increasing, but to date no candidate has been found that matches the powdery, velvety skin feel of silicones. Nylon powders and silicone elastomers therefore remain the most widely used fillers in cosmetic products, but they persist in the environment and are considered as microplastics.

Fillers are also conventionally used in exfoliating products. Exfoliation processes are mainly based on two different approaches: mechanical exfoliation and chemical exfoliation. Mechanical exfoliation involves applying an exfoliant with a granular texture and using a circular massage motion to remove dead cells and impurities. Mechanical exfoliants differ depending on the nature and size of the grains they contain (powders of fruit kernels or seeds, clays, etc.). Polyethylene or polypropylene microparticles can also be used as mechanical exfoliants; however, these formulations have a negative environmental impact related to the release of microplastics.123 

As we enter this new century, we all know that our world expects polymers to not only meet technical challenges and deliver performance, but to do so with minimal environmental impact. The question today is how cosmetic science can face these new challenges while continuing to improve performance. Finding the right balance between the eco-design of polymers and increasing performance requirements is the main challenge facing our researchers today. At present, sustainable polymer alternatives are not yet available to replace all the specific functions of many of the most widely used cosmetic ingredients; however, some examples illustrating how the cosmetics industry is progressing to meet this challenge with the research, development and incorporation of some alternative ingredients into formulations are provided below. Many of these sustainable alternatives need to be further tested and optimized and the current the range of available sustainable alternatives is limited. Although the straight-forward like-for-like substitution of petrochemical-based polymers with sustainable alternatives appears unlikely, future developments may allow sustainable polymers to replace the functions and properties of several existing polymers.

• Cationic guars

Several polymer manufacturers have developed cationic guars as an alternative to fossil-derived cationic polymers, such as polyquaternium, for use in hair conditioners. Derived from the seeds of the guar plant, this family of polymers has the advantage of being bio-based and offering good performance levels compared to traditional fossil-derived cationic polymers used in cosmetics.124 However, the quaternization process often involves certain toxic reagents and solvents, resulting in derivatives with a number of end-of-life issues (ecotoxicity and biodegradability). It is therefore essential to further develop this family of polymers (and functional alternatives) to ensure that they are produced using processes that are fully compliant with green chemistry principles and have a favorable environmental profile.

• Polyurethanes

Polyurethanes (PUs) are a class of high-performance polymers widely used in many industries, including cosmetics, for their film-forming properties. However, they are typically not biodegradable and are manufactured using an isocyanate-based process that is not in line with the principles of green chemistry.

Covestro has recently successfully launched a bio-based and biodegradable PU that displays film-forming properties that could be beneficial for use skin and hair products.125 This is a great achievement and a clear step toward sustainability. However, there is still a need to go one step further and develop PU-like alternatives that are both bio-based and biodegradable, and are produced using completely environmentally friendly chemical processes.

The use of isocyanate could be avoided by using a non-isocyanate polyurethane (NIPU) route that could allow the film-forming performance of PUs to be maintained. NIPU is based on dicarbonate derivatives and diamine precursors (Figure 15), and its use has been investigated for generating PUs for use in cosmetic in film-forming applications.

This chemistry is based on two families of monomers: dicarbonate and diamine derivatives. In this case, the polymerization mechanism is green chemistry compliant, but unfortunately the accessibility of green monomers remains a technological barrier, especially for natural diamines, which are much less abundant than natural diols. Suppliers such as Croda have proposed a diamine monomer,110,127 which is in line with sustainability commitments, but this type of polymerization does not yet offer the levels of versatility required for cosmetic and industrial applications.

• Polysaccharides

Naturally occurring rheology-modifying and water-thickening polysaccharides, such as starch, cellulose, and chitin, represent a tremendous source of innovation for the cosmetic sector and an unlimited source of raw materials. Suppliers already propose raw materials that are fully in line with the Green Science strategy, but the problem of inadequate performance or formulation difficulties with these natural polymers remain (e.g. achieving high viscosity with natural gums, and developing formulations with the same rheological profile as those containing carbomers).110 

Using a blend of natural polymers, formulators have been able to obtain textures with a good physicochemical profile and sensory properties that are well accepted by consumers, but research is needed to identify polymers based on a polysaccharide backbone with high performance, especially in oil-based media.

For this reason, these polymers must be functionalized to achieve the required level of performance. Modifying their chemical structure significantly increases their effectiveness, but often significantly reduces their biodegradability. In addition, such modifications can lead to dangerous processes (e.g. nitrocellulose formation, alkylation, or even esterification). Modification of the native polysaccharide backbone impairs biodegradability. This is the case for pullulan. Native pullulan is readily biodegradable according to OCDE guidelines.19,20 After modification of the native backbone by alkylation to produce myristoyl pullulan, the resulting polymer loses its original biodegradability.

There is consequently a need to further develop greener routes to generate polysaccharide derivatives that are both high performance and environmentally friendly.

Product end-of-life could also be a problem for polysaccharides. First, some polysaccharides are not inherently biodegradable, such as cellulose (Figure 16): only nanocelluloses are readily biodegradable, while microcellulose is not.

In conclusion, despite the extremely wide variety of bio-based backbones, it is very difficult to eco-design a highly effective biodegradable film-forming polymer based on green chemistry principles.

Another strategy to obtain a highly effective polysaccharide is to design and synthesize modified carbohydrate building blocks to access a new generation of carbohydrate-based polymers. Biocatalysis may well make this possible in the field of modified polysaccharides. This field will require the development of new tools at the interface between chemistry and biology, and even if it currently seems very ambitious to predict the synthesis of polymers, it should be noted that this objective is rapidly approaching thanks to the development of new enzymes.128,129 

• Polyhydroxyalkanoates

Several companies are currently attempting to commercialize technologies to produce a variety of polyhydroxyalkanoates (PHAs) by fermentation. Interest in this family is largely driven by the realization that these polymers are readily biodegradable. Like naturally occurring polysaccharides, PHAs have the potential to form the backbone of truly sustainable alternatives to some of the most widely used fossil-derived polymers in cosmetics. PHAs can be divided into different classes of polymers based on the length of the pendant chain: short chain length PHAs (scl-PHAs), which are mainly used as fillers, and medium/long chain length PHAs (mcl/lcl-PHAs), which show potential as film-forming agents. While the use of scl-PHA as a potential replacement for petrochemical plastics is well known, the potential use of mcl-PHA in industrial applications is still under investigation. In both cases, further research is needed to ensure that they can be produced in an environmentally friendly manner, including recovery of PHA from the microorganism, at competitive prices, with low environmental impact and ready biodegradability.127,130,131 

• Synthetic polyesters

Synthetic polyesters are a family of polymers widely used in industry, mainly for the versatility of the properties obtained, but also for the possibility of using bio-based monomers and polymerization mechanisms compatible with the principles of green chemistry. Polyesters are also of interest for cosmetics as they can be used to enhance adhesion to surfaces and to add shine to makeup formulations. Importantly, some polyesters are known to be biodegradable, while remaining chemically stable in formulations. Polyesters based on polycondensation, in particular alkyd-based polymers, are also currently being investigated.

Several low molecular-weight polyesters can be obtained from bio-based diols and diacids. Usually, biodegradability and naturalness can be achieved,132,133 but the macroscopic properties of these polyesters in cosmetic oils are limited and film properties cannot be obtained in this case.17 Several bio-based branched polyesters have been synthesized based on vegetable monomers such as natural diacids, natural fatty acids, and natural polyols. By controlling the ratio of each component, it is possible to obtain high-viscosity oils with interesting properties in terms of gloss and durability, which can be used in products such as lipsticks.134 The key parameter to control is the fatty acid ratio, which allows solubility in specific cosmetic solvents. However, increasing solubility does not provide the desired mechanical properties, and the search for rigid and multifunctional bio-sourced monomers remains crucial. Moreover, the search for polymers with high performance in terms of oil resistance (e.g. hydrophobic materials that allow final products to repel oils from food or sebum), and to this end the search for polyesters with higher mechanical modulus and film-forming properties based on 100% bio-based monomers remains a scientific challenge of great interest.

• Modified clays

Modified clays, such as modified hectorite, are widely used for their mattifying properties or as oil thickeners in makeup and facial skin care products. They are derived from renewable resources, are easy to process, and are extremely high-performance substances. However, they are typically produced through a process involving quaternization and irradiation, and the operating conditions under which they are produced are not consistent with green chemistry principles. Consequently, further research is needed to develop ingredients or blends of ingredients of mineral origin that offer the same level of performance while using more environmentally friendly production processes.

As noted in this article, the state of the art in terms of polymer application in cosmetics is challenged by the current efforts toward sustainable ingredients and formulations. This is a major change in the cosmetic industry that cannot be done by a simple trial-and-error substitution of polymers of petrochemical origin. This is an opportunity for reviewing the physical chemistry properties of polymers that are key for assuring product performance. Eco-sustainability from the origin to the end of life of polymer ingredients, including their biodegradability, is essential. To aid this transition, new modeling approaches are necessary.

A growing number of greener alternatives are already being commercialized by polymer manufacturers in response to market demand for more sustainable yet high-performance solutions in the cosmetics sector. While these developments are very encouraging, more research is clearly needed to develop polymers that are both fully sustainable (from a sourcing, manufacturing, and end-of-life perspective) and cost-competitive, while offering at least the same level of performance and safety as the most widely used petrochemical-based polymers.

The authors would like to thank Dr Emma Pilling and Dr Marielle Romet (Santé Active Edition – Synergy Pharm) for medical writing and language editing services.