Retinol is the alcohol form of the Vitamin A family, along with retinal (the aldehyde form) and retinoic acid (the carboxylic acid form).
Retinol comes in various molecular forms, and there are many forms of retinol itself and its derived esters, such as retinyl acetate, retinyl palmitate and retinyl propionate.
Currently, vitamin A derivatives for skin care mainly include: retinol, retinal (retinaldehyde), retinyl palmitate, retinyl propionate, hydroxypinacolone retinoate (HPR), etc.

Source
Retinol and its derivatives are currently prepared mainly by chemical synthesis.  They can improve the stability and bioavailability of raw materials through modification technology or encapsulation technology.

Purposes
They are commonly used as anti-aging ingredients in cosmetics.  Retinol and its derivatives have been widely recognized for their effects in reducing the appearance of wrinkles, skin laxity, uneven skin tone, and discoloration.  They can also be used clinically in the treatment of acne.

Efficacy
The major effects of retinol and its derivatives on the skin lie in promoting the metabolism of the skin epidermis, slowing down the loss of collagen, as well as reducing skin laxity and wrinkles.  In addition, retinol can help restore the normal metabolism of and thicken the skin's stratum corneum, while strengthening the skin barrier function.

Numerous in vitro experimental studies [1-2] have shown that retinol can inhibit collagenase synthesis and stimulate collagen synthesis to achieve anti-aging effects, while increasing epidermal thickness and improving the skin barrier function.

Applications
Retinol and its derivatives are mainly used in anti-aging skin care products, especially because of their role in promoting both stratum corneum renewal and collagen production.

References
[1] Varani J, et al.  Vitamin A Antagonizes Decreased Cell Growth and Elevated Collagen-Degrading Matrix Metalloproteinases and Stimulates Collagen Accumulation in Naturally Aged Human Skin1[J].  Journal of Investigative Dermatology, 2000, 114(3):480-486.

[2] Kang S, Duell EA, Fisher GJ, et al.  Application of retinol to human skin in vivo induces epidermal hyperplasia and cellular retinoid-binding proteins characteristic of retinoic acid but without measurable retinoic acid levels or irrita tion.  J Invest Dermatol 1998;105:549–56.