Quality control in retinoid-based cosmetic products
Retinoids are a group of compounds including vitamin A (retinol) and its natural and synthetic derivatives, which are biologically active. The most common natural retinoids are retinol, retinal, retinoic acid, and retinyl esters, as well as beta-carotene, which is the most common carotenoid. Retinoids participate in various biological processes, such as embryogenesis, vision, inflammation, cell proliferation and differentiation, and apoptosis.
Retinoids also have various positive effects on the skin, as their active form - retinoic acid - binds to the retinoic acid receptor located in the nuclei of skin cells, which interacts with a specific DNA sequence and regulates the transcription of "retinoid-sensitive" genes. Using retinoids in cosmetic formulations can successfully combat improper keratinocyte differentiation and proliferation, reducing the formation of micro-comedones and acne. In addition, retinoids are widely used in dermatological products that effectively address psoriasis, hyperpigmentation, and photoaging problems, as they promote collagen synthesis and inhibit its breakdown, promote epidermal renewal, and exhibit immunomodulatory, antibacterial, and antioxidant effects.
Therefore, retinoids are widely used in various cosmetic products, such as face, eye, and hand creams, body lotions, shower gels, liquid soaps, shampoos, conditioners, lipsticks, mascaras, blushes, and other products. According to the Scientific Committee on Consumer Safety and the Directorate-General for Health and Food Safety of the European Commission, the concentration of retinoids in cosmetics is limited to 0.05% retinol equivalents (RE) in body lotions and 0.3% RE in face creams and other leave-on products. In France, the concentration of retinoids in cosmetics is recommended not to exceed 0.15% RE, based on studies on the possible phototoxicity associated with retinoids. Meanwhile, in Canada, the concentration of retinoids in cosmetics is limited to 1% RE. Although most cosmetic products encourage the use of significantly higher concentrations (1-5% RE), consumers must understand that they exceed the maximum allowed vitamin A concentration in cosmetics by the European Commission (0.3%). The amount of retinoids in cosmetic products is often not declared, although some of them are advertised as high-strength products containing vitamin A. The use of retinoic acid and its salts in cosmetic products is prohibited, regardless of the concentration, mainly due to their teratogenic effect.
Why is it important to consider the concentration of retinol equivalents in cosmetic products? When used together with supplements or food that is rich in vitamin A, excessive amounts of vitamin A can be formed in the body, which is associated with various undesirable systemic effects, such as skin erythema, nausea, headaches, abdominal pain, liver damage, kidney damage, hypercalcemia, and bone abnormalities. However, the most common side effect occurs when using topical retinoids, which is called the "retinoid reaction" and manifests as a burning, itching sensation, erythema, dryness, as well as skin peeling or sensitivity to light. Unfortunately, regardless of the increasing consumer interest in cosmetics products that contain retinoids and increasing concentrations of retinoids in them, their quality and safety are not controlled and depend on the manufacturer.
We are increasingly noticing that the use of retinoids in high concentrations is encouraged in modern anti-aging cosmetics, which is associated with several negative effects. In a study conducted in 2020 , the quality of 21 commercial retinoid cosmetic products was evaluated, and the concentration and quality of retinoids were determined. Quality control of such products is particularly important for safety reasons, but it is often ignored by both manufacturers and regulatory agencies. For this purpose, an analytical method was developed that is suitable for analyzing all commonly used retinoids, including a newer derivative (hydroxypinacolone retinoate). During the study, discrepancies were revealed between the stated and determined amount of retinoids, and it was also noted that manufacturers incorrectly label retinoids on the ingredient list (INCI). The determined amount of retinoids was usually lower than the permissible maximum concentration (0.3%), but higher amounts of retinoids (up to 1.3%) were found in five products. Several violations were found in the tested retinoid cosmetics, including excessive retinoid levels, incorrect labeling, and the presence of retinoic acid. These results indicate that stricter regulation and quality control of retinoids are needed to ensure their effectiveness and safety in cosmetic products.
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 Temova Rakuša, Ž, Škufca, P, Kristl, A, Roškar, R. Quality control of retinoids in commercial cosmetic products. J Cosmet Dermatol. 2021; 20: 1166– 1175.