what causes finger fungus
Fungal Nail Infection (Onychomycosis) Overview. Fungal infection of the toenails or fingernails is caused by a fungal microbe that invades the nail bed. Fungal nail infection is also termed onychomycosis and tinea unguium. Fungal nail infection causes fingernails or toenails to thicken, discolor, disfigure, and split. At first, onychomycosis appears to be only a cosmetic concern. Without treatment, however, the toenails can become so thick that they press against the inside of the shoes, causing pressure, irritation, and pain.