Although retinoids such as Tretinoin (all-trans-retinoic acid, retinoic acid aka acidified form of vitamin-A) are very effective in the treatment of acne, the side effects to some people are not acceptable. Side effects include redness, peeling, dryness and flaking of the skin. The side effects associated with Retinoic Acid use is due to the fact that it has very strong and aggressive effect on skin cell differentiation. Retinoic acid is the form of vitamin-A that has direct effect on skin cells but if it is delivered at an uncontrolled rate, it would cause tissue irritation. Users of retinoic acid do not have a very good compliance with regards to its use mainly because of its side effects.
Milder forms of Vitamin A such as Retinyl Palmitate, Retinyl Acetate and Retinol give similar results to Retinoic Acid but has fewer side effects. It is expected that acne sufferers would be able to comply more with the use of milder topical Vitamin-A forms because its side effect is more tolerable. In keratinocytes (epidermal cells), retinyl palmitate and retinyl acetate are converted by an enzyme into retinol which is the alcohol form of vitamin-A. Retinol is then oxidized into retinoic acid. Retinoic acid would stimulate skin cell replication by attaching to retinoic acid receptors (RAR) on the outer membrane of skin cells. These forms of vitamin-A when applied topically are converted into retinoic acid at a controlled rate thus they have fewer side effects. The conversion rate of retinyl esters to retinoic acid is therefore dependent on the enzymes that exists on the skin cells.
I. Retinyl Palmitate
This is the most abundant form of vitamin-A in the human body. The body stores vitamin-A in the liver in the form of Retinyl Palmitate. Retinyl palmitate is very stable and accounts for at least 80% of the Vitamin-A that you can find in the skin. Retinoic acid in the skin can be increased by topical application of Retinyl Palmitate. This is the least irritating form of topical vitamin-A but it does not penetrate the skin very well.
II. Retinyl Acetate
Retinyl Acetate is a water soluble form of vitamin-A. It is reported to be relatively more effective than retinoic acid because it penetrates the skin more effectively. Since this form of vitamin-A penetrates the skin at a faster rate, it is more irritating than retinyl palmitate.
III. Retinal/Retinaldehyde/9-Cis-Retinoic-Acid
This is the vitamin-A form that is found on the retina of the human eye. Absorbed retinal on the skin is then converted to retinoic acid via oxidation. According to one study, topical retinaldehyde is converted by the skin to retinoic acid (active form) and at the same time it is also converted to retinyl esters (storage form).
IV. Retinol
The alcohol form of Vitamin-A. Retinyl palmitate in the liver is transformed into retinol so that it can be transported to other tissues of the human body. Most over the counter topical vitamin-A product on the market is retinol.
Efficacy
Topical retinoic acid (RA) causes irritation of the skin. To prevent this side effect, natural precursors of RA have been proposed. The aim of the present study was to compare the local tolerance profiles of retinol (ROL), retinaldehyde (RAL) and RA. METHODS: ROL, RAL and RA were studied using repeated insult patch tests for 14 days. The natural retinoids ROL and RAL do have a good tolerance profile, in contrast with the irritating potential of RA.
( Source: Tolerance profile of retinol, retinaldehyde and retinoic acid under maximized and long-term clinical conditions.Fluhr JW, Vienne MP, Lauze C, Dupuy P, Gehring W, Gloor M. Department of Dermatology, Klinikum Karlsruhe, Germany. JFluhr@compuserve.com)
References
Sorg O, Antille C, Saurat JH. Retinoids, other topical vitamins, and antioxidants. Photoaging. Marcel Dekker, 2004: 89-115.
Chiu A, Kimball AB. Topical vitamins, minerals and botanical ingredients as modulators of environmental and chronological skin damage. Br J Dermatol 2003; 149(4): 681-691.
Lupo MP. Antioxidants and vitamins in cosmetics. Clinics in Dermatology 2001; 19:467-473.
Ramos-E-Silva M, Hexsel DM, Rutowitsch MS, Zechmeister M. Hydroxy acids and retinoids in cosmetics. Clin Dermatol 2001; 19:460-466.
VARIETIES OF VITAMIN A USED IN COSMETIC PREPARATIONS APPLIED TO THE SKIN By Dr. Des Fernandes Copyright© Environ Skin Care (Pty) Ltd. 2006.
Topical Creams and Medicaments – Lotions and Potions For Skin Rejuvenation
Ms Elizabeth Tian By National Skin Centre (Singapore) Copyright (C) 1995
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