Benefit and risk of organic ultraviolet filters

Modern sunscreen products provide broad-spectrum UV protection and may cont ain one or several UV filters. A modern UV filter should be heat and photos table, water resistant, nontoxic, and easy to formulate. Identification of a substance that meets these criteria is as difficult as discovering a new drug; hundreds of new molecules are synthesized and screened before a lead candidate is identified. The most important aspect in the development of a new UV filter is its safety. In our laboratories, the safety of new ultravi olet filters is assessed by an initial in vitro screen including photostabi lity, cytotoxicity, photocytotoxicity, genotoxicity, and photogenotoxicity tests. These tests are performed in mammalian, yeast, and bacterial cell sy stems. Skin penetration potential is measured in vitro using human skin or, when required by regulations, in vivo. Because modern sunscreens are selec ted on the basis of their retention on and in the stratum corneum and are f ormulated as poorly penetrating emulsions, they generally have very low to negligible penetration rates. The safety and efficacy of UV filters are reg ulated and approved by national and international health authorities. Safet y standards in the European Union, United States, or Japan stipulate that n ew filters pass a stringent toxicological safety evaluation prior to approv al. The safety dossier of a new UV filter resembles that of a new drug and includes acute toxicity, irritation, sensitization, phototoxicity, photosen sitization, subchronic and chronic toxicity, reproductive toxicity, genotox icity, photogenotoxicity, carcinogenicity, and, in the United States, photo carcinogenicity testing. The margin of safety of new UV filters for applica tion to humans is estimated by comparing the potential human systemic expos ure with the no-effect level from in vivo toxicity studies. Only substances with a safe toxicological profile and a margin of safety of at least 100-f old are approved for human use. Finally, prior to marketing, new UV filters undergo stringent human testing to confirm their efficacy as well as the a bsence of irritation, sensitization, photoirritation, and photosensitizatio n potential in man. UV filters not only protect against acute skin injury, such as sunburn, but also against long-term and chronic skin damage, includ ing cellular DNA damage, photoinduced immune suppression, and, by extension , skin cancer. The protection provided by modern sunscreens against UV-indu ced skin cancer was shown in animal photocarcinogenicity studies and confir med by numerous in vitro, animal, and human investigations: UV filters prot ect the p53 tumor suppressor gene from damage and prevent UV-induced immune suppression. Recent studies suggest that sunscreens protect against precur sor lesions of skin cancer, such as actinic keratoses. Additional benefits of ultraviolet filters include prevention of photodermatoses, such as polym orphic light eruption, and, possibly, photoaging. Modern sunscreens are safe for children and adults. Percutaneous penetratio n and irritation rates of topically applied substances in children and adul ts are similar. The principal protective measure is to keep children out of the sun and/or to cover them with protective clothes; however, sunscreens are a safe and effective and often the only feasible defense of children ag ainst UV radiation. In conclusion, sunscreens are safe protective devices t hat undergo stringent safety and efficacy evaluation. (C) 2001 Academic Pre ss.