Moisturizer
Moisturizers or moisturisers (see spelling differences) are complex mixtures of chemical agents specially designed to make the external layers of the skin (epidermis) softer and more pliable, by increasing its hydration (water content). Naturally occurring skin lipids and sterols as well as artificial or natural oils, humectants, emollients, lubricants, etc. may be part of the composition of commercial skin moisturizers. They usually are available as commercial products for cosmetic and therapeutic uses, but can also be thrown together at home using common pharmacy ingredients.
Besides imparting or restoring normal levels of hydration to the skin, moisturizers can have several additional intended and unintended effects on their users, including building a barrier against the loss of water through the epidermis (skin), repairing scaly, damaged or dry skin resulting from external environmental aggressions or internal changes (such as in acne or naturally dry skin), repairing or postponing the aging effects on the skin, etc.

# Composition
Although simple and effective moisturisers can be prepared from two or three simple chemicals, such as stearate, olive oil, water and glycerin, commercial preparations are astoundingly complex and varied in composition and may include:
- Humectants, such as glycerin, urea, lactic acid and sorbitol;
- Natural moisturising factors (NMF) include low molecular weight substances such as ammonia, aminoacids, glucosamine, creatinine, citrate and ionic solutions such as sodium, potassium, chloride, phosphate, calcium and magnesium.
- Emollients, such as lanolin (the earliest complex organic substances used in facial and body moisturisers, which is extracted from wool). Lanolin acts as a barrier (occlusion effect) against loss of water and also as a softener of stratum corneum, by means of lubrication and smoothing. Other emollients are oil-water emulsions of varying composition and may include several esters and oils such as octyl dodecanol, hexyl decanol, oleyl alcohol,decyl oleate, isopropyl stearate, isopropyl palmitate, isopropyl myristate, hexyl laureate, and dioctyl cyclohexane.
- Emulsifier, preserving and fragrance agents are also part of commercial preparations.
Moisturisers are among the most used and prescribed products for the skin; unfortunately, the cosmetics industry often advertises loudly for scientifically unsubstantiated effects. Physicians, cosmeticians and consumers alike should be aware of the real science behind skin moisturisation, and know what is possible to achieve and what is not. For example, the addition of vitamins (A, B, C, D and E), nutritive agents, proteins and phytotherapeutic agents has been common in the industry, supposedly in order to add to the moisturiser the capability to treat several skin conditions such as cellulitis, age and photo damage, edema, loss of collagen, wrinkles, etc., with little or no scientific evidence for such.

# Adverse effects
Despite claims to the contrary by the cosmetics industry, complex moisturisers may cause a number of adverse effects, including allergic reactions to some of its components, skin irritation, contact dermatitis, characterised by redness, itching, burning and stinging sensations, or even may cause a contrary effect to the desired, i.e. they may actually increase dehydration. When used near sensitive spots, such as the eyes, lips and genitals, these effects may be exaggerated in some persons. Use of plant extracts, some alcohols and proteins may increase the danger of adverse effects. Cosmetic and therapeutic moisturisers should be accompanied by the printed formula in order to inform consumers adequately, as well as physicians, in order to easily and quickly identify the offending component.

# Reference
- Centurion, S.A. et al.: Moisturizers. eMedicine.