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Cosmetic stability predictions one of the key parameter for good quality of the product and is essential to assure the efficiency of the preservative system, and consumer safety. This study proposes the determination of cosmetics chemical stability validated by chromatography and physical measurements. Physical and organoleptic stability, important parameters in skin care products are also considered in this work. Twelve cosmetic products were stored at 25°C and 45°C during three months. According to organoleptic results, five formulas on twelve showed signs of degradation and physical instability, that can turn into unattractive product and damage their image. The same formulas have shown significant pH, viscosity and modifications. Chemical degradation and toxic byproduct identification are evaluated by analytical assay. According to analytical results, no concentration decreases have been observed for UV filters, contrary to some preservatives. First decrease has appeared for methyl paraben at Day 40 at room temperature (RT) and at Day 19 at 45°C, a 10% diminution has been observed. This decrease can have consequences on microbial safety by proliferation of microorganisms and cause skin infections after application. By the large range of product forms studied in these experimentations, the need to choose the best criteria for each formula, before any study of stability, appeared as obvious. Regarding the type of formula and the ingredient, oxidation and degradation of urea have been identified as being responsible for instability. Identification of these reactions demonstrates that determination of chemical reactions in cosmetic safety evaluation and determination of the shelf life of a product have to be studied to ensure safety. For two critical formulas: body scrub and moisturizer, theoretical period after open (PAO) were confronted with experimental determination and have not been proven. Finally, in regard to active compounds studied: methylparaben, propyl paraben, salicylic acid and benzoic acid showed diminution of concentration in time contrary to UV filters.

Stability of Cosmetic Formulations Containing UV Filters and Preservatives, Based on Physical and Chemical Parameters