Emollients are cosmetic preparations used for protecting, moisturizing, and lubricating the skin. These functions are normally performed by sebum produced by healthy skin. The word “emollient” is derived from the Latin verb mollire, to soften.
Water constantly evaporates from the deeper layers of the skin, an effect known as transepidermal water loss (TEWL). By regulating its water content, skin maintains a dry, easily shed surface as a barrieragainst pathogens, dirt, or damage, while protecting itself from drying out and becoming brittle and rigid. The ability to retain moisture depends on the lipid bilayer between the corneocytes.
Emollients prevent evaporation of water from the skin by forming an occlusive coating on the surface of the stratum corneum. TEWL is normally about 4–8 g/(m²⋅h). A layer of petrolatum applied to normal skin can reduce the TEWL by 50–75% for several hours.
Humectants also have an emollient effect, but they act differently, by drawing water into the stratum corneum.