Repeated use of surfactants contained in shampoo and kitchen detergent elicits eczema with severe itch. However, there is no therapeutic agent effective for itching and skin protection. N-Nonanoyl tryptamine is an ingredient contained in cosmetics, but its function is still unknown. In this study, we investigated the effect of N-nonanoyl tryptamine (NNT) on itch in mice with surfactant-induced eczematoid dermatitis. Sodium dodecyl sulfate (SDS) was repeatedly applied once a day to the dorsal skin of mice that had been shaved in advance. NNT was repeatedly applied twice a day to the same skin region. Repeated treatment with SDS induced eczematoid dermatitis, the decrease of the water content of the stratum corneum, and scratching, which is an itch-related behavior. The treatments of NNT before SDS treatment and at least 6 h after SDS treatment on the same day inhibited significantly these symptoms elicited by SDS, compared with vehicle treatments. These results suggest that, in addition to moisturizing the skin, NNT effectives surfactant-induced eczema and itch. Therefore, it is considered that NNT is a functional cosmetic ingredient.