Metabolism of sunscreens in various species

In order to achieve the stated SPF (2 mg/cm2) of a sunscreen preparation, about 35 ml are needed for a whole-body application for adults. If it is applied at the recommended frequency, at least twice this amount could be applied during a day at the beach. During other periods, sunscreens may be applied to sun-exposed sites such as the face, hands and arms for extended periods or used daily in cosmetic preparations. Ideally, sunscreens should remain on the skin surface, so that they can be washed off, or should be bound only to the nonviable epidermis (stratum corneum). Relatively little is known about the percutaneous absorption and metabolism of sunscreens. Since they might be used daily throughout life, it is clearly important that any interactions that sunscreens may have within viable skin and systemically should be assessed. The percutaneous absorption of sunscreens has been studied in humans and animals in vivo. Ex-vivo techniques, in which viable excised skin is used as a membrane in a diffusion chamber and test material is collected in a receptor fluid, have also been used.