What is it?
Retinol is a naturally occurring fat soluble vitamin, also known as Vitamin A. Retinol is chemically classified as a diterpenoid. It oxidizes readily and is inactivated by ultraviolet light. Retinol plays an essential role in many physiological processes in the body including proper functioning of reproductive organs and immune function. 1

Benefits:
In cosmetic formulas, retinol functions as a skin conditioning agent. It has been shown to be an effective antiaging and antiacne2 treatment. Topical use of retinol improves overall photodamage, crow’s feet, elasticity, wrinkles, brightness, and hyperpigmentation. 3 Induced production of glycosaminoglycan, which is known to retain water, as well as increased collagen production are believed to be involved in retinols antiaging effects.4 

Potential negative side effects:
The Cosmetics Ingredient Review (CIR) panel warns that retinol may cause skin irritation, allergic reaction, cause reproductive and developmental toxicity, genotoxicity, and phototoxicity. Retinol is not recommended for use during pregnancy. The CIR expert panel concluded that retinol is safe for use in cosmetics at current practices with concentrations up to 5%.5 Due to frequent side effects such burning, itching, dryness, and redness, as well as possibility of toxicity, retinol derivatives have been developed with fewer side effects.

Good for the following conditions:
Skin aging and acne in people without sensitive skin that are not pregnant. However, due to potential side effects, some may choose to avoid retinol.

Aliases:
Vitamin A, all-trans-Retinol, Alphalin, Axerophthol, Afaxin, Oleovitamin A, Alphasterol, Biosterol, 3,7-Dimethyl-9-(2,6,6-trimethyl-1-cyclchexen-1-yl)-2,4,6,8-nonatetraen-1-ol, (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraen-1-ol, and others. See PubChem for complete list of names.

References:
1) https://pubchem.ncbi.nlm.nih.gov/compound/445354#section=Depositor-Supplied-Synonyms.
2) Leyden, J. J. (1988). Retinoids and acne. Journal of the American Academy of Dermatology, 19(1), 164-168.
3) Gold MH, Kircik LH, Bucay VW, Kiripolsky MG, Biron JA. Treatment of facial photodamage using a novel retinol formulation. J Drugs Dermatol. 2013;12(5):533–540.
4) Kafi R, Kwak HS, Schumacher WE, et al. Improvement of naturally aged skin with vitamin A (retinol). Arch Dermatol. 2007;143(5):606–612. doi:10.1001/archderm.143.5.606.
5) https://www.cir-safety.org/sites/default/files/rp_buff_092012.pdf

How safe is it?

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