ERYTHEMA INDUCTION BY ULTRAVIOLET-RADIATION POINTS TO A POSSIBLE ACQUIRED DEFENSE-MECHANISM IN CHRONICALLY SUN-EXPOSED HUMAN SKIN

Background: It is generally accepted that a UVA-induced erythema is di fficult to detect except in the most sensitive individuals, Objective and Methods: As UVA effects on human skin and skin cells have been sho wn to depend strongly on anatomical body sites, UVA I, UVA I + II and solar simulator radiations were compared in their ability to induce er ythema and melanin pigmentation responses in individuals with skin typ es I-IV on both previously sun-exposed (arms, forearms, thighs) and no nexposed body sites (buttocks). Results: Erythema induction by UVA I o n previously nonexposed skin sites followed a dose response in all ski n types which was contrary to the absence of erythema induction seen o n previously sun-exposed sites, Melanin expression followed a dose and skin type response and was shown to be more enhanced in previously ex posed skin and in skin types III and IV. In contrast, UVA I + LI induc ed erythema on nonexposed skin areas and to a lesser extent on frequen tly sun-exposed skin. Melanin production by UVA I+II was similar to th at seen with UVA I alone in individuals of skin types II and III. Sola r simulator radiation was very efficient in erythema induction regardl ess of previous sun exposure of skin. Conclusions: We have found that contrary to the widespread opinion that UVA and in particular UVA I co uld not induce a significant erythema, this waveband is capable of mea surable erythema induction on skin nonexposed to sunlight. The diminis hed erythema induction by UVA I on chronically sun-exposed skin sugges ts the possibility of a defense mechanism against UVA-induced damage i n this tissue.