Sunscreens Health Article

SUNSCREENS

Sunscreens can be categorized as chemical sunscreens, physical blockers, or a combination of both. Chemical sunscreens contain UV-absorbing molecules that filter and limit the amount of ultraviolet (UV) radiation exposure at the skin. The most widely used chemical sunscreens in the United States contain para-aminobenzoic acid (PABA) or its derivatives, cinnamates, benzophenones, anthranilates, or salicylates. Some individuals develop allergic contact dermatitis to these compounds in sunscreens. These compounds predominantly absorb short-wave UV light (UVB) although chemicals that contain benzophenones and dibenzoylmethane (Parsol 1789) have also been developed recently to filter long-wave UV light (UVA).

Physical blockers utilize particles that reflect and scatter UV light. The more common physical blockers include titanium dioxide, zinc oxide, magnesium oxide, magnesium silicate (talc), kaolin, iron derivatives, barium sulfate, and red petrolatum. The older, opaque formulations had limited cosmetic appeal; newer blockers, however, have been combined with chemical sunscreens to give a more elegant appearance. In 1978, the Food and Drug Administration classified sunscreens as drugs and thus established standards for toxicity and quality control. The efficacy of sunscreens is measured in terms of the Sun Protection Factor (SPF). The SPF is defined as the ratio of the doses of artificial sunlight required to cause minimal skin redness with and without sunscreen. Individuals who burn easily, who are on photosensitizing medications, or who have light-sensitive diseases should diligently use sunscreens with SPFs between 15 and 30. Reapplication after prolonged sweating or swimming is recommended. Although sunscreens can provide protection against sunburns, its role in skin cancer protection remains a controversial issue. Some, but not all, studies have found an increased risk of cutaneous melanoma with sunscreen use. The most likely explanation is the individuals who use sunscreen tend to stay out longer in the sun, thereby increasing photocarcinogenesis.

HENSIN TSAO

(SEE ALSO: Food and Drug Administration: Skin Cancer; Ultraviolet Radiation)