More often, they are bases or vehicles for topical medication, such as in Whitfield's ointment.
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Moisturizers are used for the treatment of certain skin diseases, such as psoriasis, ichthyosis vulgaris, xerosis, and pruritus in atopic dermatitis. Many plant and animal extracts have been claimed to impart skin benefits, with little scientific evidence. Some products are marketed as having anti-wrinkle and skin enhancement effects. Moisturizer cosmetics may additionally contain antioxidants, ceramides, emulsifiers, fragrances, penetration enhancers, preservatives, and solvents. For this reason, they have essentially replaced vegetable oils in emollients and topical medication. Mineral oils and waxes are insensitive to oxidation or rancidity. Moisturizers may also be available as lotions, creams, ointments, bath oils, or soap substitutes. Other popular moisturizers are cetyl alcohol, cetearyl alcohol, cocoa butter, isopropyl myristate, isopropyl palmitate, lanolin, liquid paraffin, polyethylene glycols, shea butter, silicone oils, stearic acid, stearyl alcohol and castor oil, as well as other oils. Petrolatum is one of the most effective moisturizers, although it can be unpopular due to its oily consistency. There are many different types of moisturizers. They also help smoothen the skin by plugging gaps between dead skin cells. Moisturizers 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 moisturizer. When used in practical applications, they are almost always combined with occlusives. A study published in Skin Research and Technology in 2001 found no link between humectants and moisturizing effect. They can absorb this water from the air and moisturize the skin when the humidity is greater than 70%, but more commonly they draw water from the dermis into the epidermis, making skin dryer. Humectants are hydrophilic and absorb water. Oils naturally produced by the human body moisturize through this same mechanism. A layer of petrolatum applied to normal skin can reduce that loss by 50–75% for several hours.
Water loss through the skin is normally about 4–8 g/(m²⋅h). Ointments are more occlusive than aqueous creams, which are more occlusive than lotion. The more occlusive the formulation, the greater the effect. Occlusives form a hydrophobic coating on the surface of the skin, keeping moisture from escaping. Moisturizers modify the rate of water loss, with active ingredients of moisturizers falling into one of two categories: occlusives and humectants. The ability to retain moisture depends on the lipid bilayer between the dead skin cells. 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.
In the human body, water constantly evaporates from the deeper layers of the skin through an effect known as transepidermal water loss (TEWL). The word "emollient" is derived from the Latin verb mollire, to soften.
These functions are normally performed by sebum produced by healthy skin. A moisturizer, or emollient, is a cosmetic preparation used for protecting, moisturizing, and lubricating the skin.
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