Oct 19, - Onychomycosis, also called tinea unguium, is a fungal infection that affects either the fingernails or toenails. A fungal nail infection occurs from the overgrowth of fungi in, under, or on the nail. The same fungi that cause jock itch, athlete’s foot, and ringworm can cause nail Causes · Risk Factors · Symptoms · Diagnosis. They are also known as onychomycosis and tinea unguium. Both fingernails and toenails are susceptible to infection, which usually appears as discoloration Treatment · Home remedies · Pictures · Causes.