Skin Cancer Care Guide

UV Filter against Skin Cancer

Modern sunscreen products provide broad spectrum UV protection and may contain one or several UV filters. A modern UV filter should be heat and water resistant, non-toxic 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 synthesised and screened before a lead candidate is identified. The most important aspect in the development of a new UV filter is its safety.

In laboratories, the safety of new ultraviolet filters is assessed by an initial extensive testing on its properties as a sun screen including photostability, cytotoxicity, photo-cytotoxicity, genotoxicity and photo-genotoxicity tests. These tests are performed in mammals, yeast and bacterial cell systems and skin penetration potential is measured in vitro using human skin, or, when required by regulations, in vivo.

Because modern sunscreens are selected on the basis of their retention on and in the stratum corneum and are formulated as poorly penetrating emulsions, they generally have very low to negligible penetration rates. The safety and efficacy of UV filters are regulated and approved by national and international health authorities while Safety standards in the US, Europe or Japan stipulate that new filters pass a stringent toxicological safety evaluation prior to approval. The safety dossier of a new UV filter resembles that of a new drugs include acute toxicity, irritation, sensitisation, phototoxicity, photo-sensitisation, subchronic and chronic toxicity, reproductive toxicity, genotoxicity, photo-genotoxicity, carcinogenicity and, in the US, photocarcinogenicity testing.

The margin of safety of new UV filters for application to humans is estimated by comparing the potential human systemic exposure 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-fold are approved for human use. Finally, prior to marketing, new UV filters undergo stringent human testing to confirm their efficacy as well as the absence of irritation, sensitisation, photo-irritation and -sensitisation potential in man. UV filters not only protect against acute skin injury, such as sunburn, but also against long-term and chronic skin damage, including cellular DNA damage, photo-induced immune suppression and, by extension, skin cancer. The protection provided by modern sunscreens against UV-induced skin cancer was shown in animal photocarcinogenicity studies and confirmed by numerous in vitro, animal and human investigations: UV filters protect the p53 tumour suppressor gene from damage and prevent UV-induced immune suppression. Recent studies suggest that sunscreens protect against precursor lesions of skin cancer, such as actinic keratoses.

Additional benefits of ultraviolet filters include prevention of photo-dermatoses, such as polymorphic light eruption, and, possibly, photo-ageing. Modern sunscreens are safe for children and adults. Percutaneous penetration and irritation rates of topically applied substances in children and adults 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 often the only feasible defence of children against UV radiation. In conclusion, sunscreens are safe protective devices against a carcinogenic hazard that undergo stringent safety and efficacy evaluation.