Protection by ultraviolet A and B sunscreens against in situ dipyrimidine photolesions in human epidermis is comparable to protection against sunburn

Sunscreens prevent sunburn and may also prevent skin cancer by protecting f rom ultraviolet-induced DNA damage. We assessed the ability of two sunscree ns, with different spectral profiles, to inhibit DNA photodamage in human e pidermis in situ. One formulation contained the established ultraviolet B f ilter octyl methoxycinnamate, whereas the other contained terephthalylidene dicamphor sulfonic acid, a new ultraviolet A filter. Both formulations had sun protection factors of 4 when assessed with solar simulating radiation in volunteers of skin type I/II. We tested the hypothesis that sun protecti on factors would indicate the level of protection against DNA photodamage. Thus, we exposed sunscreen-treated sites to four times the minimal erythema dose of solar simulating radiation, whereas vehicle and control sites were exposed to one minimal erythema dose. We used monoclonal antibodies agains t thymine dimers and 6-4 photoproducts and image analysis to quantify DNA d amage in skin sections. A dose of four times the minimal erythema dose, wit h either sunscreen, resulted in comparable levels of thymine dimers and 6-4 photoproducts to one minimal erythema dose +/- vehicle, providing evidence that the DNA protection factor is comparable to the sun protection factor. The lack of difference between the sunscreens indicates similar action spe ctra for erythema and DNA photodamage and that erythema is a clinical surro gate for DNA photodamage that may lead to skin cancer.