Provided is a therapeutic agent for dermatitis which: is effective and safe for use by dermatitis patients, especially patients with atopic dermatitis； exhibits remarkable effects in severe cases in which a condition was diagnosed to be extremely difficult to treat with conventional external preparations； can be applied to affected sites such as the face or neck； and is extremely safe and effective for patients with sensitive skin and for application on children or women. Also provided is an external preparation which is effective as a skin care cosmetic that exhibits improvements of the skin such as increased firmness and reduced wrinkles, and has moisturizing and hair growth efficacy. A composition for an external preparation for the skin, especially for a therapeutic agent for dermatitis and for a skin quality improver have C-type natriuretic peptide (CNP) or B-type natriuretic peptide (BNP) as the active ingredient.
