The problem to be solved by the present invention is to provide a safe and efficacious therapeutic agent for dermatitis which is not only safe and efficacious for patients with dermatitis, in particular atopic dermatitis, but also significantly effective for severe cases that are judged to be intractable by conventional external preparations, and which is also safely applicable to affected areas such as the face and neck, as well as to subjects with sensitive skin, such as infants and females. Furthermore, the invention aims to provide an external preparation that is efficacious as skin care cosmetics having effects to improve elasticity and wrinkles of the skin, moisturizing effects, and hair-growth effects. The means for solving the problem is a skin external-preparation composition, in particular, a therapeutic agent for dermatitis or a skin texture-improving agent, having C-type natriuretic peptide (CNP) or B-type natriuretic peptide (BNP) as the active ingredient.