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February 7, 2017

Fungal Nail Infection

JAMA. 2017;317(5):546. doi:10.1001/jama.2016.20617

Fungal nail infection is the invasion of the nail by a fungus.

Fungal infection is one of the most common nail disorders in adults. It usually involves the toenails but can also affect the fingernails. Fungal nail infection is also called onychomycosis.


The symptoms of fungal nail infection include nail thickening, crumbling, and discoloration. Sometimes the skin around the nail appears thickened or scaly.

Fungal infection may affect different parts of the nail. In most cases, the sides and tip of the nail are involved first. Sometimes, the top layer of the nail is covered with white markings. In rare cases, the base of the nail is primarily affected.

Fungal nail infections are sometimes painful, and, with toenail involvement, they can cause difficulty walking.

Causes and Risk Factors

Different types of organisms may cause a nail infection. Skin fungi called dermatophytes are the most common cause, but yeasts or molds may also cause infection.

Fungal nail infections are often associated with fungal infections of the nearby skin. For example, toenail infection is often associated with fungal infection of the skin of the feet (athlete’s foot), and in these cases, the same organism may be responsible for both infections.

Other conditions that increase the risk of fungal nail infections include injury or other damage to the nail or the skin around the nail, decreased blood flow to the extremities, and diabetes. Certain conditions that weaken the body’s natural defenses against infections—such as human immunodeficiency virus (HIV) infection or use of medications that suppress the immune system—also increase the risk of infection. Some people may also have a genetic component that increases susceptibility to fungal nail infections.


Many clinicians suspect a fungal nail infection based on the nail appearance. A sample of the nail is then sometimes removed and sent for testing to confirm the diagnosis and identify the type of organism causing the infection.


Not all people with fungal nail infections require treatment, and the decision to treat as well as the type of treatment used depend on many factors including the extent of the infection, possible medication interactions, cost, and patient preference. Oral medications are often used when several nails are affected. Because some oral medications in rare instances cause liver injury, blood tests may be performed several times during treatment to monitor liver function. Topical treatments are applied directly to the nail surface and are usually recommended when only a few nails are affected. Because fingernails and toenails grow slowly, treatment may be required for several months before improvement is noted. Fungal nail infections can be difficult to treat, and complete clearance of the infection is not always possible. Recurrence of fungal nail infections is also common, and preventive strategies such as keeping the hands and feet clean and dry, avoiding sharing nail clippers or nail files, and using footwear when walking in public areas such as locker rooms or public showers may help reduce the risk of recurrent infections.

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Article Information

Sources: National Library of Medicine, British Association of Dermatologists

Topic: Infectious Disease