The group of B-complex vitamins includes 8 water-soluble vitamins (B1, B2, B3, B5, B6, B7, B9, and B12). Some of them are established and valuable cosmetically active ingredients due to their positive effects on the skin. Vitamins B3 and B5 are most often present in cosmetic products, occasionally also B6 and B12, while other B vitamins are rarely found in cosmetics. Our main purpose was to evaluate the content of the most commonly represented B vitamins (B3, B5, B6 and B12) in cosmetic products. To this end, we first developed and appropriately evaluated an analytical method based on high-performance liquid chromatography for the rapid and simultaneous analysis of vitamins B3, B5, and B6. For evaluation of vitamins B12 and B7 we used a previously developed analytical method based on high-performance liquid chromatography, which we properly validated. After market review, we selected a representative sample of 37 leave-on products in various cosmetic forms (emulsions, gels, solutions) in the price range from 0,5 to 120€/50 mL of the product. The representation of individual vitamins in the selection reflects the situation on the Slovenian market. We included also the products with declared vitamin content on the packaging. We determined the content of B vitamins in the products and checked the adequacy of their labelling. Later, we also exposed certain products to the conditions for long-term and accelerated stability testing. Most products contained vitamins B3 and B5, the determined contents for vitamin B5 were 0.14 – 5.19 % (w/w), and the contents of vitamin B3 were higher in avarage (0.03 – 11.22 % (w/w)). The contents of vitamins B6, B7 and B12 were determined in 1 product with labeled contents (determined contents of B6: 0.557 % (w/w) and B12: 0.00088 % (w/w), B7 was not detected). We found that a higher price of the product is not (necessarily) associated with a higher content of vitamins and consequently with a better effect of the cosmetic product. 9 products had labeled content of B vitamins – the results showed that the determined content in 3 products deviated from the labeled one, in two products it was lower by about half. The results of a one-month stability study showed that vitamin B3 (in all but one of the tested products) was stable at both 20 ␃ and 40 ␃, and the stability of B5 was affected by elevated temperature. However, a higher price of the product was not associated with better stability of vitamins in the products. Vitamins B6 and B12 were both represented only in 1 product, so the observed instability of both vitamins at elevated temperature cannot be generalized.
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