The category of color cosmetics referred to as foundations, also known as bases, strives to achieve a complex mix of functional, sensorial and aesthetic effects. These all-over facial cosmetics aim to hide minor skin imperfections like wrinkles and blemishes; to even and modify the skin color of the face; and to alter the light reflection capability and luminosity of the face and neck—all while maintaining a natural-looking and velvety appearance.
During application, a foundation must spread easily and accurately shade the face contour, especially when the adopted color is different from the natural skin tone. The consumer typically expects a foundation to last throughout the day or event, i.e., 5–16 hr; it should leave a thin, colored film that is stretchable and adaptable to deformations of the skin, for instance, to hide uneven textured, aged skin. In addition, it should be resistant to sweat and sebum, resilient to mechanical abrasion and comfortable to wear. The foundation’s color should perform well under different lighting conditions such as sunlight or artificial light and once dry, the film should withstand a sudden rain or unexpected tears; at the end of the day, however, the makeup should be as easily removed as it was applied. The safety of the foundation also must be guaranteed, especially considering the potential catalytic effect of iron oxide pigments. These can accelerate the reaction between environmental oxygen and sebum squalene, resulting in squalene peroxide, a strong irritant.1
Physical Forms and Characteristics
Product forms: Both o/w and w/o emulsions share the color foundation market, and within these two categories, all viscosity values are represented. However, foundations are always characterized by a high yield point in order to avoid the settling of suspended pigments, in consideration of their high specific weight. Evaporation of volatiles after application to the skin is favored by the relatively high temperature of the skin surface. Fine tuning the evaporation speed of the solvents to shade along the facial contour can be accomplished through the precise dosing of hydrotropes, as is described later.
In addition to emulsion product forms, aerosol foundation sprays and foams, cream-to-powder and whipped foundations, roll-on and sponge-applied foundations, and aqueous and anhydrous molten lipid gels have been produced by creative formulating. In all cases, these vehicles keep finely dispersed pigments and fillers in suspension to contribute to coloring and adequate opacifying effects.
Site variability: Foundations are applied to a number of skin sites although mostly on the face; application to the legs is limited. These sites exhibit a variety of characteristics, with different areas of the face being dry or oily, having more or less hair—i.e., at the jawline and hairline, and having varying degrees of elasticity. For this reason, the physical forms of foundations attempt to address the behavior of the skin involved. In general, formulations containing a volatile ingredient, e.g., water or volatile silicone, are preferred because they minimize possible application mistakes by evaporating from the application site.
Acidity in foundations: The pH values for foundations are generally neutral but o/w emulsions are sometimes slightly alkaline when they contain emulsifiers with alkaline salts of fatty acids. In spite of their known limits, soap-based emulsifiers offer an important advantage: the “transient emulsifier” effect. Immediately after the application of such emulsions, the acids contained in the skin mantle, mainly lactic and PCA, neutralize the alkaline soap, thereby destroying the emulsifying agent. This provides a long-lasting effect by increasing the water resistance properties of the film.
Sensorial properties: The sensorial properties of foundations act as a non-verbal guide for the consumer. As the texture of the foundation becomes thicker with application due to the fluid ingredients being absorbed or evaporating, and the powders in the remaining fluid increasing accordingly, the user knows to begin shading the edges of the face. A velvety final touch also informs the consumer that complete distribution has been achieved. A good skin feel tells consumers they have chosen the right product for their skin type. Visual evaluations during the day reassure the consumer of the lasting properties of the applied layer. Indeed, makeup products are a challenge from the performance evaluation aspect—their properties are evaluated by users during, immediately after and many hours following application. Moreover, a critical visual evaluation is often conducted by the user’s family, colleagues and friends.
A general emulsion foundation is shown in Formula 1. The structure of this three-phase foundation is both a pigmented emulsion and a suspension emulsion—i.e., the micronized pigment particles are suspended in the emulsion, since suspensions are less stable than standard emulsions due to gravity. Furthermore, suspended pigments and solid fillers interact strongly with the ingredients of the emulsion, especially with emulsifiers, making the design of the formula much more complicated than standard emulsions. While the base formulation shown can be altered with special additives, e.g., emollients, silicone gums, sunscreens, sebum absorbers, anti-aging actives, moisturizers, hydrolyzed proteins and soft focus particles, as noted, separately addressing the ingredients in a foundation does not account for their interactions. Foundations generally are not made by the average properties of their ingredients, but rather by the complexity provided by ingredient interactions. Nevertheless, key notes related to the main ingredients will be described here.
Water and hydrotropes: A balanced amount of water is essential for the adequate wetting of porous and hydrophilic pigments and fillers, the complete swelling of polymers, and the correct drying time after distribution over the skin. Hydrotropes such as glycerin, propylene glycol, butylene glycol and betaine finely tune the evaporation speed, making foundation shading onto the skin smooth and versatile.
The formula equilibrium between water and hydrotropes should be controlled to allow the user to distribute a thin, even layer of foundation all over the face, including on the contours. The main drawback of an incorrectly designed foundation is the chromatography of the iron oxide shades that occur at the facial contour. Chromatography involves the different porosity of iron oxide and titanium dioxide particles, their different polarity and absorption capabilities, and their particle size ranges. The result is a division of the pigments at the facial contour, with the red pigment adhering to the skin and the yellow pigment being easily distributed.
Pigments: Pigments used in foundations are internationally allowed.2 They are made of trivalent hydrated iron oxides in all the colors of rust, from dark yellow to brick red, sienna, umber and black. In this last case, the equivalent mineral is called magnetite, and the oxidation states of its iron atoms are two and three. Only in special cases, e.g., camouflage products, will small amounts of anhydrous chromium oxide green be used. The development of colors to match skin tones and modify skin luminosity is ensured by the white pigment titanium dioxide, of which both the anatase and rutile allotropic forms are used. All pigments used in foundations exhibit variable and competing capabilities for the absorption and adsorption of the vehicle, i.e., the water and oil phases and the emulsifier. The formulation challenge is to adjust the vehicle composition for varying shades—up to 30 in the worst cases, to achieve consistent application performances.
The introduction of coated pigments in cosmetics around 30 years ago noticeably simplified the formulation and production difficulties of foundations. By equalizing the surface of different pigments, coatings allow the formulator to produce different shades while keeping the general vehicle composition constant. Moreover, coatings eliminate the need to mill pigments, a common need with uncoated pigments, in order to disrupt their aggregates. Coatings avoid the catalytic superficial activity of iron oxides, lowering their adsorption of skin sebum and reducing the sensorial heaviness of the formula by hindering the stuffing of pigment granules by the oils and fats of the emulsion. Coatings such as silicone, alumina, polyurethane or alkaline di-hydroxystearate also create increased transparency and see-through optical properties. This can aid foundations formulated with iron oxide and titanium dioxide, as the opacity and dull appearance of iron and titanium oxides are a drawback when a natural or nude look is desired.
In relation to color, lakes usually are not used in foundations because their chemical and physical properties are different from those of pigments, and their colors are too brilliant and different from those of natural skin tones.
Fillers and optical interference solids: Fillers play many important roles in foundations, as they do in many other color cosmetic products. Since they are insoluble in the vehicle, faintly white, and more or less transparent, fillers modify the formulae where they are introduced. Fillers such as silicone cetearyl dimethicone copolymersa can provide slip and a silky feel while reducing oil and shine. The most traditional fillers in foundations include hydrophilic kaolin, which provides water absorption and skin adhesion, and lipophilic talc, which is used for its transparency and slip.
Hydrated silica gels are compounded in mixed modern fillers like hexamethylene diisocyanate (HDI)/trimethylol hexyllactone crosspolymer (and) amorphous silicab. Polymethyl methacrylatesc, d provide soft touch and velvety feel. Boron nitrides, based on their particle size, impart silky gloss and lubricity. These are just a few examples of fillers, where the chemical nature, the physical surface characteristic, the morphology and roundness, and the softness and preferential interactions with some formula ingredients and the skin surface determine a wide array of performances. Recent developments employ soft focus effect particles and synthetic phlogopites to modify skin luminosity and perceived wrinkling.
Oils and fats: Blends of polar oils are preferred ingredients for the lipid phase of emulsion foundations for their good pigment wetting properties with adequate affinity for the skin. Their fluidity offers easy distribution and their interfacial tension toward the skin, as modified by emulsifiers, should be low to ensure adequate skin wetting. The refractive index of such materials should be low enough to avoid excessive shine on the skin. Therefore, branched chain and iso-esters generally are used at low percentages. Unsaturated (oleic) chains are often avoided due to their easy uptake of malodors, especially in the presence of iron oxides.
Silicones can be part of the oil phase, with volatile silicones being preferred. The combination of oils with different polarities can put the stability of the formula at risk because of different preferential absorptions by the surfaces of pigments and fillers. The solid part of the lipid phase, when required, is generally comprised of superior fatty alcohols or stearic acid for their emulsion stabilization properties and their capability to form a thin layer over the skin. Waxes, the typical layering ingredients employed in makeup, are scarcely used in emulsion foundations except for solid rounded silicone or jojoba beads of micrometric size, for sensorial reasons.
Emulsifiers: The amount of emulsifier used in emulsion foundations is far higher—from 20–50% more, than in other types of emulsions. The reason is due to the capability of pigments to firmly bind discrete amounts of surfactants. Insufficient contribution by emulsifiers leads to uneven distribution of the pigments in the product container, resulting in flotation and precipitation. In addition, it causes non-homogeneous spreading over the skin. This is because during application of the foundation, superficial skin lipids are emulsified and compete with the pigments in binding the emulsifiers. The result is a segregation of the different pigment shades at the facial contour.
As previously mentioned, saturated—i.e., solid, alkyl chain emulsifiers are preferred, frequently associated with partially saponified stearic acid. Recently, a vegetal-derived inulin lauryl carbamatee was developed that provides emulsification advantages at low use concentration; 0.5–2.0% calculated on the amount of oil and solids phases. This material does not influence emulsion viscosity and is not influenced by the polarity of the oil phase. Also, since it interacts with incident light, transparency on the skin is increased and the covering power of the pigments is decreased. Moreover, their adhesion performance on skin is improved. Other polymeric emulsifiers are also used, when compatible with the pigments.
Thickeners and rheology agents: Achieving the desired rheology with foundations requires a mixed system of ingredients to combine shear thinning properties with adequate suspension capability, especially when the formulation is a fluid foundation. Usually, blends of swollen aluminum silicatesf, together with hydrophilic polymers like hydroxyethyl cellulose, create an associated structure in the fluid that exhibits suspension power for micronized powders but also provides enough fluidity to make the product spreadable on the face. Aluminum silicates also impart a matte effect on skin and a velvety touch when dry. Some grades of purified celluloseg and cellulose microfibers provide similar performance to aluminum silicates. Oil phase thickeners are also used, especially for the external phase of w/o formulae. They are usually based on lipid swollen hectorite,h dextrinj or long chain wax estersk and provide body and texture to emulsions. An accompanying effect is the increased covering power and trace homogeneity.
Film-formers: To assure long-lasting wear and adequate water-resistance in foundations, film-formers are often used. These materials must be compatible with the pigments so as to avoid the formation of lumps, which can form when the polar groups in the film-formers come into contact with the pigment surface. Members of the polyacrylate family are frequently used due to their film-forming, non-tacky and wear-resistant properties. More recently, polyurethane dispersions have shown the capability of providing good water-resistance and non-transfer effect at 5% solids.m Sequestering agents: Together with antioxidants, sequestering agents are important for blocking the pro-oxidant action of iron oxides in suspension. Aside from being traditional chelating agents, polyphosphonic acidsn have also shown the ability to improve dispersion and aid in pigment wetting.
Other additives: Since foundations are applied to the skin in thicker layers and are intended for longer wear than typical skin care products, formulators often add advanced skin care ingredients to them. Such functional additives provide moisturization, anti-aging properties, elasticity, sun protection, anti-free radical efficacy, etc. Their compatibility and stability with pigments should always be checked.
Reproducing the Formulation
Although formulating an efficacious foundation can be difficult, it can be more difficult to reproduce the same shade in successive batches. There are many reasons for this but the main factors are pigment size and agglomeration, the variable wetting of powders, different saponification degrees of stearic acid, incomplete de-aeration, etc. In addition, an important dilemma is whether the pigments and fillers should be added to the water or lipid phase first.
Usually, better reproducibility is obtained by adding previously milled pigments to the oil and emulsifier base under vacuum to eliminate the entrapped air and to wet the pigments. Hot water phase addition follows. Temperatures for making foundations are slightly higher than for other emulsions, and emulsification times are longer. This is due to the pigments consuming/binding discrete amounts of emulsifiers. Even with maximum process accuracy, however, shade correction is frequently necessary. This can be better managed by preparing monochromatic foundations in advance so that their addition cannot influence the delicate balance between the solids and the vehicle, laboriously obtained on the bench.
Aside from checking the usual physical parameters such as pH, density and rheology, evaluating a foundation also requires control of the correct pigments and fillers to achieve dispersion and lack of agglomerates, as observed by microscope. A trained colorist evaluation of the color, both in mass and when applied to skin, is necessary under standard illumination lamps to identify small differences among shades. Water-resistance can be measured by applying the product onto glass surfaces or in vivo, with methods that are similar to water-resistance SPF evaluations. Special claims, such as reducing the signs of aging, involve evaluations by trained judges of pictures taken of volunteers who are wearing the product. Probably much more difficult to support would be a claim such as “makes the skin breathe.”
- M Ottaviani, T Alestas, E Flori, A Mastrofrancesco, CC Zouboulis and M Picard, Peroxidated Squalene Induces the Production of Inflammatory Mediators in HaCaT Keratinocytes: A Possible Role in Acne Vulgaris, J Invest Dermatol 126 2430–2437 (2006)
- International Colour Handbook, 4th ed, AP Rosholt, ed, Cosmetic, Toiletry and Fragrance Association, Washington, DC USA (2007) pp 20
This content is adapted from an article in GCI Magazine. The original version can be found here.