Photobiology, photodermatology and sunscreens: a comprehensive overview. Part 2: topical and systemic photoprotection.

Sun exposure of the skin triggers several inflammatory pathways via a multitude of photochemical and photobiological effects. Furthermore, local and systemic immune suppression develops. The main clinical effects of UV exposure can be classified schematically into immediate, including sunburn, tanning, vitamin D production and exacerbation of inherited and acquired photosensitive skin disorders and long-term, including solar ageing and skin cancer. The protection against solar radiation is afforded by a healthy behavior of reasonable sun avoidance and the use of topical sunscreens as well as topical and oral antioxidants. However, users of sunscreen products should be able to choose correctly the most convenient product according to their needs. In Europe, the sun protection factor (SPF) and the UVA-protection factor (UVA-PF) are labeled to indicate the degree of protection against UVB and UVA, respectively. However, dermatologists must be aware that the present knowledge of UV effects on human skin needs to be clarified and several regulatory issues of photo-protection remain to be clarified and standardized. Finally, much work is needed to improve water resistance, spreadability, transparency and homogeneity of the sunscreen agents.