In the human body, water constantly evaporates from the deeper layers of the skin through an effect known as transepidermal water loss (TEWL). By regulating its water content, human skin naturally maintains a dry, easily shed surface as a barrier against 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.<unk> s modify the rate of water loss, with active ingredients of<unk> s falling into one of two categories: occlusives and humectants. Occlusives form a coating on the surface of the skin, keeping moisture from escaping. The more occlusive the formulation, the greater the effect. Ointments are more occlusive than aqueous creams, which are more occlusive than lotion. Water loss through the skin is normally about 4–8 g/(m²⋅h). A layer of petrolatum applied to normal skin can reduce that loss by 50–75% for several hours. Oils naturally produced by the human body<unk> through this same mechanism. Humectants absorb water. They can absorb this water from the air and<unk> the skin when the humidity is greater than 70%, but more commonly they draw water from the dermis into the epidermis, making skin dryer. A study published in Skin Research and Technology in 2001 found no link between humectants and moisturizing effect. When used in practical applications, they are almost always combined with occlusives.<unk> s often contain water, which acts as a temporary hydration agent as well as a way for the absorption of some components and evaporation of the<unk> .
Moisturizer
Deodorant
Dermal adhesive
Disinfectant
Antiseptic
Surgical lubricant
Fungicide
Insect repellent