Vitamin A was the first vitamin approved by the (US) Food and Drug Administration as an anti-wrinkle agent that changes appearance of the skin surface and has anti-aging effects. Vitamin A is in a group of fat-soluble substances and belongs to the category of retinoids.
Apart from retinol, that group includes structurally related substances with the biological properties of retinol. Since the biological activity of the substances differs, for the purpose of standardization, it is given in retinol equivalents. Vitamin A and its derivatives are among the most effective substances slowing the aging process. Retinoids regulate the cell apoptosis, differentiation and proliferation. Anti-wrinkle properties of retinoids promote keratinocytes proliferation, strengthen the protective function of the epidermis, restrain trans-epidermal water loss, protect collagen against degradation and inhibit metalloproteinases activity. Retinoid activity is related to high affinity for nuclear receptors: RAR – retinoid acid receptors and RXR – retinoid X receptors.
The term “Retinoid” refers to the synthetic and natural analogues of vitamin A. Retinoids are a class of compounds derived from vitamin A or showing structural and/or functional similarities to vitamin A. According to the latter definition, retinoids are molecules that can bind to and activate the appropriate nuclear receptors and to induce transcription of relevant genes either directly or after metabolic transformation. Retinoids are widely applied in cosmetics being a potent dermatological agent used in acne, psoriasis as well as other skin diseases.
Retinol is most frequently used in cosmeceutical treatment. It is very stable in product formulations and well tolerated. It provides better effects than retinoic acid applied in equivalent doses. Retinoic acid proves to be approximately 20 times more powerful than retinol. Firstly, retinol is converted to retinoic acid through a two-step oxidation process. Retinol has an ability to bind to the retinoic acid receptors.
Retinal is the aldehyde formulation of vitamin A, i.e. the oxidized form of retinol. Retinal is used in cosmeceuticals, however, its efficacy in the skin treatment is limited. Similarly to retinyl esters, it is a stable derivative of vitamin A but it only mildly improves wrinkles and the skin texture. As compared to retinoic acid, it is less irritating and well tolerated. It is used to improve signs of photoaging.
Retinyl esters, such as retinyl acetate and palmitate, are commonly used in cosmeceuticals. They are very stable but first they need to be converted to retinol by cleavage of the ester bond, and in the subsequent stage into retinoic acid. It results in decreased effectiveness of anti-wrinkle properties (smaller increase in the epidermal thickness) as compared to retinol and retinoic acid.
There are numerous publications on efficacy of various derivatives of vitamin A used in treatment of juvenile acne, acne vulgaris and other types of acne as well as in treatment of diseases related to keratosis disorders, the so-called ichthyosis and psoriasis. There are reports describing effects of skin care preparations containing maximum 0.3% of retinol on the skin condition.
Retinol and their active metabolites such as retinal, tretinoin, isotretinoin and alitretinoin belong to a group of first-generation retinoids. Retinol has the ability to effectively penetrate the stratum corneum (lipophilic nature of retinoids). Age, cellular metabolism, cardiovascular function, stratum corneum thickness, level of hydration and analysed area of the face are important factors in mature skin therapies.
NOT MY OWN WORK - Taken from:
Zasada M, Budzisz E. Retinoids: active molecules influencing skin structure formation in cosmetic and dermatological treatments. Postepy Dermatol Alergol. 2019 Aug;36(4):392-397. doi: 10.5114/ada.2019.87443. Epub 2019 Aug 30. PMID: 31616211; PMCID: PMC6791161.
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