Assessment and clinical implications of absorption of sunscreens across skin

Topical sunscreen products are widely used for protection of the skin against the harmful effects of exposure to ultraviolet radiation. Sunscreen agents are incorporated into many everyday-use cosmetics as well as so called 'beach' products. An ideal sunscreen product will provide effective protection against UV radiation with minimal skin absorption of the active ingredients. There is now clear evidence that a common sunscreen chemical, benzophenone-3, is absorbed systemically following topical application to the skin. Other more lipophilic sunscreens are absorbed into the skin, but penetration to deeper tissues and the cutaneous circulation appears to be limited. However, the extent to which sunscreens that are absorbed into the stratum corneum are absorbed to deeper tissues and the systemic circulation over time is currently unknown. The formulation vehicle in which the sunscreen is presented to the skin has a significant effect on absorption into and through the skin. Alcohol-based formulations appear to increase sunscreen absorption. In addition, some sunscreen chemicals may enhance the skin absorption of other sunscreens when applied in combination. Clearly, further research into the influence of sunscreen and formulation properties on skin absorption could lead to optimal design of sunscreen products with respect to efficacy and minimizing absorption. Despite the extensive use of sunscreen products, there have been few reports of adverse effects, and these tend to be limited to acute dermatitis and allergies. Some recent reports have raised concerns that sunscreen chemicals may damage tissues, particularly in the presence of UV radiation. Further research into the toxicity of sunscreens is urgently required. Given the information currently available and the importance of protecting the skin against sun damage, there is no clear justification for restricting the use of sunscreen products at this time.