the difference between an emollient and an occlusive is the molecular weight of the material. Examples of this are low molecular weight hydrocarbons and dimethicones that spread and absorb easily. They are often used for their ability to soften and smooth skin and impart a silky skin feel. Other classes of emollients include fatty alcohols and triglycerides, which are a key source of fatty acids for the skin. Examples of these include cetyl or cetearyl alcohol, cetylcaprylic/capric triglyceride, or oils such as grapeseed, soybean, or sunflower seed oil (Figure 5). Sunflower seed oil (SSO) is a triglyceride precursor to alpha-linoleic acid, an essential fatty acid that is incorporated into stratum corneum ceramides. The type and level of emollient is determined by the consumer needs – the relevant benefit and the clinical need as well as the desired sensory.The efficacy of a basic moisturizer is determined by the levels of humectants, occlusive, and emollients. A good moisturizer needs a balance of the three. High humectant lotions restore moisture levels to skin but cannot immediately decrease trans-epidermal water loss. High emollient or occlusive creams can immediately reduce TEWL but it takes some time for the skin hydration levels to be restored. It should, therefore, not be assumed that a cream containing high levels of occlusives or emollients is automatically more efficacious. A combination of these ingredients at adequate amounts is necessary to replenish moisture and maintain it creating an environment where the skin barrier can be repaired. This combination can be designed in a cream or a lotion since the thickness can be manipulated independent of efficacy. A final point to be made is that glycerin, petroleum jelly, and dimethicone are amongst the most commonly used, safest, and most beneficial ingredients for the skin.Emulsifiers and Polymers
Moisturizers are usually emulsions or kinetically stabilized colloidal suspensions of two immiscible liquids meaning there is no appreciable phase separation and the in-use experience remains consistent over the product’s usable lifetime. Emulsions require the use of emulsifiers for stability. Emulsifiers can range from simple monomeric surfactants to much larger polymeric surfactants, particles, and lamellar liquid crystal aggregates.An interesting property of emulsifiers is that they usually have long carbon chains like skin lipids, which makes it possible for an emulsifier to also impart skin benefits. In fact, the closer the chemistry of the emulsifier is to skin lipids, the more skin benefit can be imparted. Long chain emulsifiers, identified on an ingredient label as “palmitic” or “cetyl” (16 carbons or C16), “stearic” or “stearyl” (C18), and “behenic” or “behenyl” (C22), are compatible with and beneficial to skin, help maintain emulsion stability, and are not irritating. Stearic acid, a fatty acid with a C18 chain and carboxylic acid head group, is a good example of an emulsifier with skin benefits that Unilever uses extensively. Fatty acids are an integral component of the lipid matrix, and topically applied stearic acid has been demonstrated to incorporate into the lipid matrix improving the quality of the stratum corneum.11, 12
Another class of materials used to improve the stability, impact thickness and texture, and modify sensory feel of moisturizers is polymers. These could include synthetic polyacrylate type polymers or natural ones like starch (a polysaccharide based polymer). The feel and look of emulsions changes dramatically depending upon the polymer and emulsifier used. For example, culinary enthusiasts are aware that using a starch versus gelatin results in radically different textures. Similarly, in cosmetics, availability of novel polymers and emulsifiers have provided the formulator with a unique ability to modulate the feel and texture of moisturizers independent of its efficacy.