Measurement of in vivo sunscreen immune protection factors in humans

This study investigates the level of protection provided by sunscreens agai nst solar-simulated UV radiation-induced immunosuppression in humans, The i n vivo immune protection factors (IPF) of two broad-spectrum sunscreens wer e determined by assessing their ability to prevent UV-induced suppression o f nickel contact hyper-sensitivity (CHS) in 15 nickel-allergic volunteers. Each volunteer,vas irradiated on unprotected skin of the back with differen t doses of UV daily for 4 days. Multiples of these UV doses were concurrent ly delivered to sunscreen-treated sites on the contralateral back. Nickel p atches were then applied to both irradiated sites and adjacent, unirradiate d control sites. Nickel-induced erythema at each site aas measured 72 h lat er with a reflectance spectrometer, Comparison of the nickel reactions of i rradiated and unirradiated skin revealed linear UV dose-responses for immun osuppression in both unprotected and sunscreen-treated skin. The minimum le vel of immunosuppression that can be reliably detected with this method is 20%. Therefore, the UV dose that reduces mean nickel CHS by 20% is the mini mal immune suppression dose (MISD). Sunscreen IPF were determined by dividi ng the mean MISD of sunscreen-treated skin by that of unprotected skin. The sunscreens, with sun protection factors of 9 and 24, had IPF of 6.5 and >2 5, respectively.