Onychomycosis means fungal infection of the nail. It is the most common disease of the nails and constitutes about a half of all nail abnormalities.

This condition may affect toenails or fingernails, but toenail infections are particularly common. The prevalence of onychomycosis is about 6-8% in the adult population. Onychomycosis caused by dermatophytes is also known as tinea unguium (tinea of the nails).

Very common fungus infections of the nails, causing thickening, roughness, and splitting, often caused by Trichophyton rubrum or T. mentagrophytes, Candida, and occasionally molds. Synonim: ringworm of nails.