A nail fungal infection is also called onychomycosis. It becomes more common as a person grows older. It is a condition that is rarely felt by children. Onychomycosis may affect the toenails or fingernails and it may spread from one toe or fingernail to another.
Microscopic organisms that are known as fungus cause this condition. Fungus thrives in a dark and warm environment. A group of fungi known as dermatophytes is responsible for most cases of nail fungal infections. However, yeasts and molds may also cause this infection.