Fungal infections of the skin are caused by microscopic organisms that live on the hair, nails (onychomycosis), mouth (angular cheilitis/oral thrush) and outer skin layers of the groin, feet and skin folds. They are quite common. Although fungal infection of the toe nail poses no medical harm, it can cause the nail to lift off of the nail bed where debris can build up and stunt nail growth. Treatments include topical and systemic anti-fungal medications.