Retinoids are common ingredients in care and treatment products for acne prone skin, as they effectively inhibit the development and reduce the number of lesions. In addition to retinoids (retinol, retinal, retinyl palmitate and retinyl acetate), topical benzoyl peroxide (BP), which has keratolytic, antibacterial and anti-inflammatory effects, is more commonly used in acne therapy. Due to a different mechanism of action, using a combination of retinoid and BP could achieve a more effective acne treatment. As we did not find data on their compatibility in the available literature, the main objective of the diploma thesis was to evaluate the compatibility of selected retinoids and BP. For this purpose, we used previously developed analytical method, based on high-performance liquid chromatography. The assay method was optimized in the direction of green chromatography, evaluated, and had its stability indicative nature confirmed by means of stress tests. This was followed by the development and optimization of sample preparation for the extraction of retinoids from four cosmetic products, with a quantitatively stated content of retinol or hydroxypinacolone retinoate on the packaging. The compatibility of retinoids and BP was first evaluated in solutions and then in tested cosmetics. We evaluated the effect of BP addition in different concentrations, which were adjusted to the determined retinol contents in the cosmetic products and BP concentrations in acne treatment products. The effects of temperature and the addition of antioxidant and / or water on the stability of retinoids in the presence of BP were also evaluated. We found a decrease in retinol content in all samples. The rate of retinoid degradation was mainly influenced by BP concentration. With higher concentrations, the retinol content decreased more rapidly, and the solutions were less stable. The retinol degradation process was slowed by a lower sample storage temperature (5 °C). Their compatibility was also affected by the medium, with aqueous solutions of retinol without added antioxidant butylhydroxytoluene being the least stable. By evaluating their compatibility in cosmetic products, we came to similar conclusions. In all products, the content of both retinoids decreased, faster degradation was detected with a larger addition of BP. We also confirmed a greater extent of retinoid degradation in products at higher temperatures. Based on the obtained results, it can be concluded that the considered retinoids are not compatible with BP, as even the lowest tested concentration of BP causes their instability and rapid decay.
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