Parrish J A, Zaynoun S, Anderson R R
J Invest Dermatol. 1981 May;76(5):356-8. doi: 10.1111/1523-1747.ep12520019.
For fair Caucasian skin, the minimal delayed erythema dose (MED) 24 hr after exposure to broadband UVA is about 1200 times greater than the MED of broadband UVB, for both single and multiple daily exposures. Repeated daily exposure to doses less than MED results in cumulative effects manifest by gradual lowering of the daily dose threshold for delayed erythema and pigmentation induced by UVA or UVB. At threshold doses, UVB is more erythemogenic than melanogenic; the opposite is true for UVA. Repeated daily UVA exposure greatly enhances melanogenesis such that markedly suberythemogenic exposure doses of UVA result in true melanogenesis.
对于白皙的高加索人种皮肤，无论是单次还是每日多次暴露于宽带UVA后24小时的最小延迟红斑剂量（MED），都比宽带UVB的MED大约高1200倍。每日重复暴露于低于MED的剂量会导致累积效应，表现为UVA或UVB诱导的延迟红斑和色素沉着的每日剂量阈值逐渐降低。在阈值剂量下，UVB引起红斑的作用比引起黑色素生成的作用更强；而UVA则相反。每日重复暴露于UVA会极大地增强黑色素生成，以至于明显低于引起红斑剂量的UVA暴露也会导致真正的黑色素生成。
