Overview of Onychomycosis

Onychomycosis is a fungal infection that causes fingernails or toenails to thicken, discolor, disfigure, and split. If the problem is caused by a bacterium, the condition is called paronychia.

The nails of people with onychomycosis are initially a cosmetic concern. Without treatment, however, the nails can become so thick that they press against the inside of the shoes, causing pressure, irritation, and pain.

Causes of Onychomycosis

The primary fungi that cause onychomycosis are Trichophyton rubrum and Trichophyton mentagrophytes. They are dermatophytes (fungi that infect hair, skin, and nails) and feed on keratinized (nail) tissue. The infections they cause are normally confined to the nails, but occasionally spread to the surrounding skin.

Another type of onychomycosis is caused by yeast (Candida albicans or Candida parapsilosis). These infections are less common and produce similar symptoms.

Paronychia infections are caused by bacteria such as Staphylococcus, Streptococcus, and Pseudomonas. In most cases, paronychia infections can be differentiated from onychomycosis by the inflammation they cause to the skin adjacent to the nail.

Treatment for Onychomycosis

Onychomycosis is difficult to treat because nails grow slowly and receive very little blood supply. However, there have been recent advances in treatment options, including oral and topical medications. Oral antifungal medications usually are administered over a 3 month period.

Two available brands include Lamisil® and Sporanox®. These medications are fairly safe, with few contraindications; they should not be taken by patients with liver disease. Before prescribing one of these medications, physicians often order a blood test to make sure the liver is functioning properly.

Topical antifungal treatment (Penlac®) consists of a nail lacquer that is applied daily to affected nails. This medication does not have any contraindications but it may irritate surrounding skin in rare cases.

Because nails grow very slowly, it typically takes 6 months to a year for the nail to regain a healthy, clear, thin appearance. However, onychomycosis is an ongoing fungal infection and patients with the condition should seek treatment.

Diabetic Complications of Onychomycosis

Patients with diabetes commonly develop onychomycosis because blood circulation is poor in the extremities, and the body's ability to fight infections is compromised. Small cuts, infections, and foot injuries can have serious consequences for diabetics. Recent studies have shown a higher rate of amputation in diabetics with onychomycosis compared to those without the infection. It is important to inspect the feet closely each day and work with a physician on a program of thorough foot care.

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

Published: 01 Jan 2000

Last Modified: 17 May 2011