Hyaluronic acid
Hyaluronic acid (HA) is a naturally occurring skin substance with the ability to imbibe water up to 1,000 times its weight. It is an excellent and powerful humectant with non-adhesive texture. HA is costly but many affordable cosmetic products contain HA. It is my favorite cosmetic ingredient.
Urea
Urea is another humectant with similar components to NMF. In the 1940, it was widely used in hand moisturizers. Some studies reported that combining urea with hydrocortisone or retinoic acid, etc. increased its permeability. Topical application of 3% urea cream did not change transepidermal water loss (TEWL) but application of 10% was reported to decrease TEWL.
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α-Hydroxy Acid (AHA)
α-Hydroxy acid (AHA) has humectant functions and normalizes the keratins to strengthen the stratum corneum. It also effectively decreases keratinization of the skin. AHA was one of the first humectants introduced to the cosmetics market. Malic acid derived from apples, tartaric acid derived from grapes and citric acid also have the actions of AHA. High-concentration AHA or BHA removes the epidermal keratinocytes and induces epidermolysis. At low concentrations, they directly affect the granular layer, reduces the cohesiveness of keratinocytes to induce exfoliation and thins the stratum corneum. Thinning the stratum corneum makes the skin more supple and revitalizes the stratum corneum to result in a more youthful looking skin.
Emollient
An emollient smooths the skin and fills the space of lost keratinocytes to soften the skin texture. Emollients smooth the uneven borders between keratinocytes and strengthen their cohesiveness. This smooth surface reduces friction and enhances light refraction, giving the skin a gentle sheen. Most emollients have both humectant and occlusive actions. Lanolin, mineral oil, and petrolatum are occlusives with emollient functions.
Image 2. Actions of an emollient in the skin.
Shea butter
Shea butter (Butyrospermum parkii) is natural fat obtained from shea or karite trees. Recent studies have reported the anti-inflammatory actions of shea butter. It can be found in many skin and hair care products. Its powerful emollient effect sufficiently hydrates the skin. Shea butter is also widely used in treatment of atopic dermatitis, xerosis cutis, acne scar and striae alba.
-To be continued-
