Onychomycosis, fungal infection of the nails, often stems from untreated athlete's foot or tinea manuum (fungal infection of the hands). Although it can appear in younger children, it is much more common in adolescents and adults. People who have their nails manicured often, particularly when the cuticles are trimmed, are more susceptible to nail infections.

There are four main forms of this disorder. The most common is distal subungual onychomycosis. At first, the nail thickens and becomes brittle. The infection can spread to the entire nail, discoloring, thickening, and lifting it.

Candida onychomycosis is caused by the yeast candida. Symptoms include detachment of the nail, reddening, and swelling.

In white superficial onychomycosis, a white brittle coating appears on the nail surface while the underlying structure remains intact.

The fourth and least common form is proximal subungual onychomycosis. The fungal growth spreads outward from the cuticle. This appears most often in people with AIDS and seems to be a result of reduced immune system response. The doctor may recommend that the patient undergo testing for human immunodeficiency virus (HIV, the virus that causes AIDS).

Not all thickened and discolored nails are caused by fungal infection. Psoriasis, eczema (dermatitis), and some inherited disorders can cause similar nail damage. Accurate diagnosis depends on microscopic examination of the debris after application of potassium hydroxide and heat to the specimen.

The hard surface of the nails usually prevents penetration by topical medications, so doctors usually prescribe oral antifungals. Treatment may require removing part or all of an affected nail.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 01 Sep 2000

Last Modified: 05 Jan 2015