Sensitivity to sunburn is associated with susceptibility to ultraviolet radiation-induced suppression of cutaneous cell-mediated immunity

Skin cancer incidence is highest in white-skinned people. Within this group , skin types I/II (sun sensitive/tan poorly) are at greater risk than skin types III/IV (sun tolerant/tan well). Studies in mice demonstrate that ultr aviolet radiation (UVR)-induced suppression of cell-mediated immune functio n plays an important role in the development of skin cancer and induces a s usceptibility to infectious disease. A similar role is suspected in humans, but we lack quantitative human, data to make risk assessments of ambient s olar exposure on human health. This study demonstrates that ambient levels of solar UVR, typically experienced within 1 h of exposure to noonday summe r sunlight, can suppress contact hypersensitivity (CHS) responses in health y white-skinned humans in vivo (n = 93). There was a linear relationship be tween increase in erythema and suppression of CHS (P < 0.001), and a modera te sunburn (two minimal erythema doses [2 MED]) nias sufficient to suppress CHS in all volunteers by 93%. However, a single suberythemal exposure of e ither 0.25 or 0.5 MED suppressed CHS responses by 50 and 80%, respectively, in skin types I/II, whereas 1 MED only suppressed CHS by 40% in skin types III/IV. The two- to threefold greater sensitivity of skin types I/II for a given level of sunburn may play a role in their greater sensitivity to ski n cancer.