Long-wave UVA offers partial protection against UVB-induced immune suppression in human skin

Ultraviolet‐B (UVB, 280–320 nm) interferes with the generation of cell‐mediated immunity to contact allergens applied epicutaneously on the irradiated site. To investigate whether pretreatment with UVA‐1 (340–400 nm) protects against the UVB‐induced immune suppression we sensitized human volunteers with diphenylcyclopropenone (DPCP) on normal buttock skin (n=12), on UVB‐irradiated buttock skin (n = 21), on buttock skin pretreated with UVA‐1 (n= 12), and on buttock skin pretreated with UVA‐1 and thereafter irradiated with UVB (n=22). Sensitization on UVB‐irradiated skin reduced the immunization rate to DPCP compared with sensitization on non‐irradiated skin (p