IL22 and skin disorder: It should be mentioned that, FICZ, as an endogenous UVB photoproduct (28), has been found to be closely related to human skin physiology (163) that could limit the production of IL-17 and IL-22 in mouse dermatitis models by activating the AhR receptor (142, 161), this barrier-protecting effect may partially explain why UVB phototherapy is effective in treating AD and psoriasis (164, 165).