The CTFA dictionary defines emollients as: ‘‘cosmetic ingredients which help to maintain the soft, smooth and pliable appearance of the skin; emollients function by their ability to remain on the skin surface or in stratum corneum to act as lubricant, to reduce flaking, and to improve the skin’s appearance.’’ Emollients are also described as refatting additives or refatteners in the case of bath products. The word refattener refers to substances improving the lipid content of the upper layers of the skin; they prevent defatting and drying out of the skin. Several emollients showing strong lipophilic character are identified as occlusive ingredients; they are fatty/oily materials that remain on the skin surface and reduce transepidermal water loss. The CTFA dictionary defines occlusives as: ‘‘cosmetic ingredients which retard the evaporation of water from the skin surface; by blocking the evaporative loss of water, occlusive materials increase the water content of the skin.’’

Overall, emollients and refatteners are oils and fats derived from natural origins or obtained by chemical synthesis; they are classified in nonpolar (paraffins and isoparaffins) and polar substances (esters and triglycerides); their chemical structure influences the interaction with the skin surface and affects their sensorial properties. As a class, they comprise lipids, oils and their derivatives, fatty acid esters, lanolin derivatives, and silicones and their organofunctional derivatives. Originally, emollients were developed for use in leave-on skin care products; formulation technology can aid the deposition of refatting additives on the skin from wash-off products and avoid that they rinse off with the surfactants; nevertheless, the large dilution factor in both products remains a significant hurdle for skin end benefit perception (except in bath oils).

Emollients and refatteners will provide after feel, but will also influence skin feel during usage, foam feel, and most of the time foam quantity and quality. The more hydrophobic the refattening additive, the more negative its impact on flash foam generation, foam quantity, and stability. In other respects, the more lipidic the material, the better its skin substantivity, and the easier the efficacy documentation; proof and substantiation of claims is of more and more importance in the frame of the Sixth Amendment of European legislation for cosmetics and toiletries.

Source: Handbook of Cosmetic Science and Technology - André O. Barel, Marc Paye, Howard I. Maibach