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Rethinking Retinoids

By: Noureddine Mriouah
Posted: July 30, 2012, from the August 2012 issue of Skin Inc. magazine.
skin care client using professional retinoid-based cream

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Retinol is a 20-carbon molecule that consists of a cyclohexenyl ring, a side chain with four double bonds (all in trans configuration) and an alcohol end group, hence the name “all trans retinol.” The oxidation of the alcohol end group in retinol results in the formation of an aldehyde (all trans retinaldehyde), which can be further oxidized to a carboxylic acid (all trans retinoic acid or tretinoin).

Of all the members of the retinoid family, only retinoic acid is biologically active. Retinol, the most common form of retinoid in skin care, is obtained either directly from certain foods, such as fish oil and liver, or indirectly from carotenoids, which are found mainly in fruits and vegetables, such as carrots, melons, apricots, mangoes, spinach and tomatoes. With the help of enzymes, it is then converted to retinal for membrane transport. To be effective, retinal is then converted into retinoic acid for targeted cell delivery.

Retinoids are required for a vast number of biological processes. In particular, they are involved in embryogenesis, reproduction, vision, growth, inflammation, cellular differentiation, proliferation, apoptosis, the immune system, reproduction, and the proliferation and differentiation of the epithelia.

Applications in dermatology and cosmetology

Retinoids have been used for many years in the treatment of actinic keratosis, seborrhea, acne vulgaris, ichthyosis, psoriasis, lichen, precancerous lesions and skin melanomas, and UV-induced skin aging. The mechanisms of action of retinoids on the skin are still the subject of research, but certain facts have been clearly established. Regarding the epidermis, retinoids play an important role in the proliferation of epidermal cells, keratinization and desquamation. At the dermal level, they influence fibroblast proliferation and collagen metabolism. During the inflammatory response, they show immune-modulatory activity and may prevent tumor growth.

Although retinoids—and retinol in particular—are among skin care’s most popular ingredients, they nevertheless pose certain problems to product developers. Quick to degrade, difficult to deliver and irritable in high concentrations, retinoids require additional considerations to ensure optimal performance and minimal irritation. Such added attention, however, comes at a price. As a result, skin care suppliers are often forced to choose between an enhanced ingredient and keeping production costs manageable.

Formulating with retinoids