Diaper dermatitis (DD) is a common disease in the first two years of life, although incontinence DD is seen in all ages including the elderly. Its pathogenesis is not uniform since irritant, allergic, and infectious factors can be involved. Diagnosis is visual except for atypical cases. After birth, the skin adapts from aquatic to terrestrial life. The skin-gut microbiome develops. The focus of the prevention of DD lies in the stabilization of epidermal barrier function and a healthy microbiome. Treatment depends on DD etiology. It includes skincare, hygienic measures, and medical therapy.