In vitro sunscreen photostability testing: detecting instability to correctly predict in vivo sunscreen performances

Photostability is a key factor in the overall performance of sunscreens. Organic filters tend to physiologically decay over time due to UV photo-decay. This effect is the normal result of the protection granted by sunscreen filters, and is to be considered normal. The physiological photodegradation of sunscreens, and the related loss of efficacy, however, can be increased beyond optimal levels by complex filter-filter and filter carrier interactions.