Onychomycosis is an infection of the nail caused by a fungus. The infection occurs more often on toenails than fingernails.

The fungi that cause onychomycosis thrive in warm, moist environments. Factors that may contribute to onychomycosis include:

• Injury to the nail
• Exposure to warm, moist environments, like locker rooms
• Damp socks
• Tight fitting shoes
• Poor nail care

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors for onychomycosis include:

• Age: 60 or older
• Smoking
• Type 1 or Type 2 diabetes
• Circulatory disorders, such as peripheral vascular disease
• Immune system disorders, such as human immunodeficiency virus (HIV) infection

Onychomycosis can affect one or more nails.

Symptoms include:

• Thickened nail that is difficult to cut
• Brittle or ragged nail
• Discolored or unsightly nail
• Pain of the finger or toe with ordinary activities

Your doctor will ask about your symptoms and medical history, and perform a physical exam. You may need to be referred to a doctor who specializes in skin and nail disorders (a dermatologist). The doctor may scrape or clip the nail to send a sample for testing.

Tests on the nail sample may include:

• Culture
• Microscopic examination

Since nails grow slowly, it can take up to a year to have a completely clear nail. Onychomycosis can be difficult to treat and may return after treatment. Talk with your doctor about the best treatment plan for you. Treatment options include the following:

• Prescription antifungal medications taken by mouth (Note: Some people cannot take antifungal medications. Tell your doctor about any other medications you are taking and any medical problems you have.)
• Creams and ointments
• Antifungal nail lacquer

Surgery to remove the nail is sometimes performed in severe cases of onychomycosis. A new nail grows in its place.