The healthy nail is protected from microbial invasion: the nail plate surface is smooth and adherent to the nail bed, the cuticle seals the skin of the proximal nail fold to the nail plate, and nail growth permits elimination of exogenous material deposited on top or below. Nail infections occur when the biological agent has a strong invading capacity (as in the case of non-dermatophyte molds) or, more commonly, when the nail is predisposed to invasion since it is damaged in some way or when there are systemic or genetic diseases or other conditions that favor infection. Predisposing factors influence the occurrence and severity of the infection, its response to therapy, and recurrence after cure. Acute bacterial paronychia is frequent in children and is rarely a cause of medical consultation. When paronychia has a recurrent course, the possibility of herpes simplex infection should be considered, and Tzanck smear and cultures should be done. Warts are the most common viral infection of the periungual tissues and can be difficult to manage when they are multiple and involve several digits. Fungal nail infections are due to dermatophytes in more than 80% of the cases and commonly present as distal subungual onychomycosis and white superficial onychomycosis.