COMPARATIVE STUDY OF ERYTHEMA RESPONSE TO UVA RADIATION IN GUINEA PIGS and HUMANS*,†

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Abstract
Abstract— Cutaneous erythema resulting from UVB radiation has been extensively studied in both humans and experimental animals; however, although there have been several investigations defining UVA erythema in humans, there have been no comprehensive reports using an animal model. Accordingly, studies were designed to assess UVA erythema in terms of time of onset; time of maximum reaction; and fluence‐response relationships in albino guinea pigs and to compare these with similar studies in humans.Two high intensity Hg vapor lamps containing iron and gallium halides were used as UVA light sources. Both have sufficient fiuence rates (190 to 260 W m−2) so as to allow convenient exposure times for delivery of UVA erythemogenic fluences. UVA fluences of 20 times 104, 40 times 104 and 60 times 104 J m−2 were administered to 58 humans and 51 Hartley‐strain albino guinea pigs.Data obtained in humans indicate that UVA erythema develops immediately after irradiance with a maximum erythema peak occurring in 6 to 12 h and markedly diminishing by 24 h. The minimal fiuence required to elicit erythema responses in Type I and Type II individuals was found to be approximately 40 times 104 J m−2 of UVA when observed at 6 h, a fiuence about 1000 times greater than that used to elicit UVB erythema.Studies in 51 guinea pigs demonstrated erythema immediately after irradiance, with a peak between 8 to 12 h, and a marked decrease in 48 h. The fiuence of UVA required to elicit erythema was similar to that required in humans. The two different light sources provided comparable data per unit exposure and were essentially similar to a Xe lamp.These data from both humans and guinea pigs strongly support the concept that UVA erythema can be assayed in guinea pigs and correlated with humans.