Decreased indole-3-aldehyde was observed in both lesional and non-lesional skin of AD patientsTopical and orally administered indole-3-aldehyde attenuated MC903-induced AD-like dermatitis in mouse and decreased expression of IL-4, IL-5, IL-6, IL-13, and TSLPTopically administered indole-3-aldehyde reduced inflammatory cell infiltration in mice. Here, IL4 is linked to dermatitis.