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Read this article and more in the September 2023 digital magazine.
Waxy and polymeric ingredients in color cosmetics are generally not highly visible. They do, however, empower such functions as film forming (mascara, eyeliner), volumizing (mascara, lip-gloss), transfer resistance (foundation, lipstick) and applicability (compact powder, lipstick).
Waxes stabilize emulsions mainly of the w/o type. Their structure makes the incorporation of oils easier, avoiding product sweating and improving application and appearance on the skin. In foundations, waxes are used to tune the spreading of the colored layer. Waxes are also of critical importance to lipsticks – their blend and composition determine the structure of the stick and its drop point. Waxes also form the structure of eye and lip crayons, among other cast products.
In lip gloss, waxes provide film forming and adhesion properties and because discrete amounts of lip products are swallowed the waxes used are food grade. In mascara, waxes provide plasticity, volume and flexibility in the film applied to lashes.1 Here, the right equilibrium in wax amount and composition is necessary to obtain a balance of firmness and deformability in the colored film, to avoid fragility without losing lash thickness improvement.2
In face powders and eye shadows, wax blends are introduced into binding systems since these cosmetics require mechanical resistance to withstand being dropped or struck. At the same time, the waxes also do not decrease slip or make the product too rigid.
Besides waxes, swellable polymers also lend supporting roles to formulas. They influence flow properties and modify the reactions of formulas to externally applied stress including gravity. They are used to gel solutions and thicken suspensions and emulsions. Polymers also support the dispersion and suspension of insoluble ingredients and largely increase emulsion stability. In makeup, polymers function as binders, thickeners, film formers or agents to impart water resistance.
Choosing the right polymer as a rheology modifier requires considering the physico-chemical characteristics of the modifier and the formula. Some choice-influencing factors are: the nature of the phase where it is added (lipids or aqueous); the type of formulation (gel, emulsion, anhydrous product, etc.); and the presence of surfactants, cationic substances and polar solvents such as alcohols.
This column reviews types of waxes and polymers, their structures and functions. It also explores their properties in terms of color cosmetic product development and highlights those that are most appropriate for “green” formulas.
The World of the Waxes
Waxes are solid ingredients, pliable at room temperature and characterized by high melting points. By chemical definition, they are esters of long-chain fatty acids with long-chain fatty alcohols. In cosmetic terms, waxes are defined as high melting point substances with “waxy” properties; i.e., plastic, dull, hard, non-slippery, chemically inert, stable, film forming and partially lubricating. Due to their long alkyl chains, they are not soluble in water.
The inertness of waxes serves unique protective functions in the vegetal world. Indeed, many plants produce small amounts of wax in their tissues, pollen and seeds. Frequently, waxes are a water-proofing secretion of leaves, roots, fruits and desert plants.3 They hinder bacterial penetration because these microorganisms do not have enzymes capable of digesting the waxes to permit them to cross the protective layer.
Waxes can be natural or artificial. Specifications for natural and bio-derived products generally allow for the use of animal (e.g., beeswax, lanolin wax, etc.) and vegetal waxes (e.g., carnauba wax, candelilla wax, etc.). However, specifications generally exclude those of mineral origin obtained from oil fractional distillation (e.g., paraffin wax, microcrystalline wax, ozokerite, etc.) and all synthetic waxes.
For cosmetic use, natural waxes require accurate refining processes. Many natural waxes are also certified as organic; Table 1 provides a summary of waxes that can be used in green products. The following is an overview of various waxes.
Table 1
White beeswax: Beeswax is produced in beehives from honeybees (genus Apis) starting from sugars (fructose, glucose and saccharose). Beeswax composition is highly complex – made of more than 300 ingredients. Fatty acids (C16-32), esters with C18-30 alcohols, fatty acids C16-32 and alkanes C22-34, with high molecular weight, are the main components of beeswax, followed by superior fats and alcohols. Good percentages of hydrocarbons, free fatty acids and other substances are also present.
Beeswax is normally used in a bleached form, which has a whitish color, while virgin beeswax is yellow.4 Almost all lipsticks contain beeswax. Indeed, it is a safe ingredient even when swallowed and is classified as a generally recognized as safe (GRAS) substance for food uses.5 Emollient and protective, beeswax helps to form a thin film on the lips and is a good stabilizer in w/o emulsions.
Lanolin: Lanolin is a mix of high molecular weight esters (> 80%), acids and fatty alcohols, fats, sterols and hydrocarbons. It is obtained through the purification of wool wax. Its sterols content imparts lenitive properties. In addition, it can absorb up to 40% w/w water. Today it is used more in pharmaceuticals than in cosmetics due to its animal origin.
Carnauba wax: Carnauba wax is obtained from the leaves and sprouts of the Brazilian palm Copernicia cerifera. It consists of 80% esters, while the remaining part is made of linear saturated free fatty acids, free alcohols, triterpenes and linear hydrocarbons. Carnauba is added to other waxes to increase their melting points, hardness and luster and to decrease stickiness, plasticity and the tendency for crystallization.
In eye and face makeup, carnauba wax forms a water repellent film and counteracts the solvent action of soaps. It may come into contact safely with the mucous membranes of the eyes, nose and mouth, as well as facial skin for long periods. Carnauba wax is a GRAS food additive and is also available from organic farming.
Candelilla wax: Candelilla wax is obtained from several species of Euphorbiaceae. Its main constituents include hydrocarbons (50-53%), esters and linear saturated free fatty acids. It is a hard and fragile wax, used as a structuring agent in anhydrous sticks. Candelilla imparts good luminosity and adhesion properties to makeup formulations. It is also classified as a GRAS substance and is authorized for the food industry.
Japan wax: Obtained from mesocarps of the fruits of Rhus succedanea (Anacardiaceae), Japan wax is a vegetal emollient made of palmitic acid and other long-chain fatty acids. It is classified as GRAS and is used in cosmetics – mainly lipsticks.
Orange peel wax: Orange peel wax is a soft, plastic, yellow wax obtained from the rind of orange fruit (Citrus aurantium dulcis) as a byproduct of the production of essential oil and orange terpenes. Its chemical composition is similar to that of lanolin, essentially making it a vegetal version of the animal wax.
Orange peel wax consists of a complex mixture of special esters, free fatty acids, hydrocarbons, free sterols and alcohols. In addition, the wax contains small amounts of flavonoids, carotenoids, glycolipids and phospholipids that are well-known for their antioxidant, anti-inflammatory, antimicrobial and sunscreen properties.
Olive unsaponifiable wax: The separation and purification of waxes present in the unsaponifiable fraction of olive oil yields an ingredient comprising vegetal wax esters (70-90%), squalene (10-30%), phytosterols (0.3-0.8%) and tocopherols (0.3-0.7%). Phytosterols provide the wax with moisturizing, emollient and lipo-reducing properties. The wax is highly massageable with average greasiness but not sticky. The final skin feel is soothing and emollient.
Formula 1 shows a pearly lipstick obtained using a combination of waxes of both natural and non-natural origin. Here, the addition of olive oil wax gives the product better spreadability and a softer feel to the lips. Furthermore, the wax is able to enhance the performance of the pearl, providing a glossier appearance.
Formula 1
Jojoba Oil and Esters
Jojoba oil is derived from the seed of the shrub Simmondsia chinensis. Its description as an oil can be misleading as it is not a blend of triglycerides but is made of fluid esters. Jojoba oil’s composition includes linear bi-unsaturated monoesters derived mainly from the condensation of the unsaturated acid eicosaesenoic and docosaesenoic with unsaturated alcohols C20/C22. Therefore, it is a liquid wax at room temperature, is not prone to rancidity, and it is brilliant and emollient on the skin.
Jojoba oil used as a natural and stable alternative to some waxes and traditional vegetal oils. Several blends of semi-synthetic esters have been obtained from refined jojoba oil. Depending on their chemical composition and firmness at room temperature (from fluid to pasty), they exhibit good pigment wetting power and increase the break resistance of lipsticks.
Other Waxes
Rice bran wax: This wax is an ester wax obtained from rice bran. It can be used a structuring agent for oil gels like lipsticks and mascara.
Berry wax: Berry wax is a soft wax obtained from the fruits of the sumac tree (Rhus verniciflua) and is an off-white, 100% vegetable wax. It is used in emulsions as an emollient and in stick preparations as a gelatinizing agent for oils, particularly castor oil and other ester oils.
Sunflower wax: Sunflower wax is obtained by refining sunflower seed oil. It consists mainly of long-chain wax esters and is free from glycerol esters and other esters or poly-alcohols. Sunflower wax modifies the rheology of oil gels and w/o emulsions and stabilizes stick preparations.
Mimosa wax: Mimosa wax is extracted from flowers of mimosa (Acacia decurrens). It consists mainly of natural long-chain esters and phytosterols. It improves viscosity in anhydrous systems and w/o emulsions and improves product adhesion on the skin with moisturizing effects.
Essential flower waxes: Finally, flower essential waxes from narcissus, jasmine and rose are extracts obtained via enfleurage. This technique consists of macerating the petals in a blend of fats and waxes, which obtains perfumed waxes.
Formula 2 outlines a mascara that emphasizes eyelash volume and thickness. In this application, high melting point waxes can impart a lengthening effect. Low melting point waxes such as tea wax are more suitable for volume-enhancing effects, giving a creamy texture and thicker film. In addition, film-forming polymers (described next) are essential to create a film on the eyelashes that boosts length, water resistance and creates definition. In general, polymers accelerate the drying time; this feature can be exploited when combining polymers with waxes.
Formula 2
Polymers
Polymers can be divided into two main groups: water swellable polymers and oil thickeners. Thickeners of aqueous phases can be further subdivided into two categories: 1) inorganic polymers, e.g., clays like bentonite (aluminum silicate, hectorite), magnesium silicate and magnesium-aluminum silicate; and 2) organic polymers, e.g., natural and modified polysaccharides (natural gums), semi-synthetic molecules (alginates, propylene glycol alginate) and synthetic molecules (poly-oxy-poly-propylenes, polyethylene glycols and vinyl polymers). Specific examples are detailed next.
Thickeners of oil phases, especially those used in cast products, provide a plastic structure that is easily spreadable over the skin, wear resistant and non-deformable under the application stress. Lipid thickening, when high amounts of waxes or other high melting point materials are not used, is possible with a few green thickeners; see Table 2 for example rheology modifiers for green formulations.
At one time, natural products were the most used but were progressively abandoned, mainly for their variable viscosity values and ease of microbial spoilage. These were substituted by synthetic and semi-synthetic polymers built around the formulators’ needs. With the resurgence of naturals, however, vegetal polymers have been reclaimed – although taking greater care in terms of purity level specifications and molecular weight variations.
Table 2
Natural gums: Among the natural gums, xanthan is the most successful. It is an efficient suspending agent for insoluble actives and pigments. It also thickens with pseudo-plastic behavior that is stable in a wide range of temperatures and pH levels.
Carrageenans: Carrageenans are complex polymers extracted from red seaweeds (e.g., Chondrus crispus) found in the cold waters of the Atlantic coast. They are used as aqueous thickeners and film formers to obtain elastic, non-sticky gels with refreshing effects, suspending action, bio-adhesion and some co-emulsification. They easily release perfumes and flavors and are massageable.
Cellulose derivatives: Cellulose derivatives are naturally derived polymers used as nonionic thickeners. Their swellable nature coordinates water molecules into gel structures. They provide excellent flow and spreading properties. Several grades of cellulose derivatives exist, e.g., ethyl cellulose, each with characteristic rheological behavior. Aqueous solutions of hydroxyethyl cellulose, for example, are not influenced by high salt concentrations whereas their viscosity is influenced by weak acids and alkali.
Magnesium aluminum silicate: Derived from a natural smectic clay, or Fuller’s earth, magnesium aluminum silicate is treated with water to optimize its purity and performance. Smectic clay is appreciated for its ease of swelling in water and its rheology in aqueous systems. Several grades have been developed, each with characteristic rheology, chemical and colloidal properties. These clays show good adsorption, emulsion and suspension stabilization; synergy with natural gums; good compatibility with anionic and nonionic ingredients; and stability over time. Magnesium aluminum silicate also helps to improve product spreadability and actively reduces the stickiness of gums.
Other Thickeners
Clays such as hectorite are mineral gels. Chemically modified clays (where alkali is substituted by quaternary ammonium ions) are more efficient thixotropic agents but they are not accepted in natural products.
Hydrogenated castor oil is obtained from the controlled hydrogenation of the triglyceride blend (85-90% from ricinoleic acid, C18:1) extracted by cold pressing from Ricinus communis seeds. It is especially used in stick products.
Finally, metallic stearates or behenates, behenyl alcohol and smoked silica may contribute to system stability and structuring. However, they cannot be strictly considered as true thickeners of oil phases.
Formula 3 provides an example of a poured eye shadow. This compact paste is easily absorbed and distributed on the skin. It is blendable and has a silky touch. Here, the presence of synthetic wax (glyceryl behenate/eicosadioate) helps to disperse the pigment and provide for the uniform application of the product.
Formula 3
Conclusion
In review, polymers and waxes play an essential role in the formulation of cosmetic products. In general, they are fundamental for the thickening, stabilization, dosage and application of a product. For example, the structure of a lipstick and its dropping point, and the volumizing effect of a mascara or its resistance to humidity are all fundamental characteristics that are significantly influenced by these ingredients.
Having in-depth knowledge of these two classes of ingredients makes it possible to regulate almost every functional parameter of cosmetic products. However, the current market demand for only natural substances presents new challenges that are perhaps even more difficult to face in the color cosmetics category.
Read this article and more in the September 2023 digital magazine.
References
1. Valsesia P., Pirovano C., Crusco C., Hanno I., Vitali A., Saligari F., Bettinelli S., Depta G. (2017). Shape-adapting film formers based on linear siliconic polyurethanes. 24th IFSCC Conference.
2. Hollenberg, J. (2000). Color cosmetics. Harry’s Cosmetology, Ch. 26, 8th edn. Chemical Publishing Co Inc. Available at https://www.chemical-publishing.com/v/vspfiles/assets/images/pages%20from%209780820603728_txt.pdf
3. Lecomte, J. (July, 2009). Vegetable waxes: Sources and applications, OCL - Oilseeds and Fats, Crops and Lipids. 16(4):262-266. Available at https://www.researchgate.net/publication/288220401_Vegetable_waxes_Sources_and_applications
4. Kurek-Górecka, A., Olczyk, P. (2022). Bee Products and Their Applications in the Food and Pharmaceutical Industries. Pages 25-62. Available at https://www.sciencedirect.com/book/9780323854009/bee-products-and-their-applications-in-the-food-and-pharmaceutical-industries
5. GRAS Substances (SCOGS) Database (accessed July 2023). Available at https://www.fda.gov/food/generally-recognized-safe-gras/gras-substances-scogs-database
