Stress produces free radicals which can be counteracted by antioxidants. Depending on the antioxidant status of the skin and blood the radical formation as a response on a definite stress induced by UVA light differs in amount and typ. If reactive oxygen species predominate, the radical formation can be compensated by the antioxidant system. But when lipid oxygen species prevail, the point of positive stress is exceeded. The method can be applied on excised skin and blood samples.
An experimental method for the determination of the sun protection factor of sunscreen is developed at the Department of Skin Physiology at the Clinic of Dermatology and Allergology at Charité – Universitätsmedizin. The measurements are not based on the development of a sunburn as biological response of the skin to sun radiation. They will be carried out in vivo on volunteers by reflectance spectroscopy.