Onychomycosis (Toenail Fungus)


What Is It?

Toenail fungus, also called onychomycosis, is a relatively common condition that disfigures and sometimes destroys the nail. Onychomycosis can be caused by several different types of fungi (microscopic organisms related to mold and mildew). These fungi thrive in the dark, moist and stuffy environment inside shoes. As they grow, they feed on keratin, the tough protein that makes up the hard surface of the toenails. In most cases, the fungus belongs to a group of fungi called dermatophytes, which include Trichophyton rubrum and Trichophyton interdigitale. Other, less common causes of onychomycosis include yeasts and molds.

Toenail fungus affects 2 percent to 18 percent of all people worldwide and 3 percent to 5 percent of people in the United States. It is relatively rare in children, affecting only about one out of every 200 people younger than 18. However, the likelihood of getting toenail fungus increases with age, so that up to 48 percent of people have at least one affected toe by the time they reach age 70. Although 2.5 million Americans see a podiatrist annually for treatment of toenail fungus, many more are infected but never seek help. Some people consider toenail fungus just a cosmetic problem, and don’t bother seeking treatment.

Almost anyone who wears tight-fitting shoes or tight hosiery has an increased risk of developing toenail fungus, especially if they also practice poor foot hygiene. Wearing layers of toenail polish, which doesn’t allow the nail to breathe, is another risk factor. Also, because toenail fungi may spread from foot to foot on the floors of showers and locker rooms, fungal infections of the toenails are especially common among military personnel, athletes and miners. The condition also tends to affect people with chronic illnesses, such as diabetes or HIV, as well as people with circulatory problems that decrease blood flow to the toes. However, many people have no clear risk factors.

Of all the toenails, those on the big toe and little toe are the most likely to develop a toenail fungus. This may be partly because the big toe and little toe are constantly exposed to the mild trauma of friction from the sides of shoes.


When a toenail develops a fungal infection, it typically turns yellow or brown and becomes thick and overgrown. Foul-smelling debris also may accumulate under the nail, especially at the sides and tip. As the infection continues, the nail either may crumble gradually and fall off or become so thick that the affected toe feels uncomfortable or painful inside shoes.

In a less common variety of toenail fungus, called white superficial onychomycosis, the nail turns white rather than yellow or brown, and the surface becomes soft, dry and powdery.


After you describe your foot symptoms, your doctor will ask you about any factors that might increase your risk of toenail fungus. These include a high-risk occupation, sports participation, tight-fitting shoes or hosiery, poor foot hygiene or use of heavy toenail polish. Your doctor will also ask whether you have a history of poor circulation, diabetes, HIV or any other illness that might decrease your resistance to infection or interfere with blood flow to your toes.

Because psoriasis sometimes can cause nail problems that look similar to a fungal infection, your doctor may ask whether you or anyone in your family has psoriasis. In some people with psoriasis, the nails are the only part of the body affected; the skin is largely spared. Also, it is possible for psoriasis and a fungal infection to affect the same toenail.

If you and your doctor decide that this nail problem is important, he or she will examine your affected toenail or toenails. To confirm that you have a fungal infection, your doctor will take small samples of the affected nails and send them to a laboratory. The nail samples will be examined under a microscope and will be checked for fungi and other microorganisms.

Expected Duration

Toenail fungus rarely heals on its own. It is usually a chronic condition that gradually progresses to involve more and more of the nail. Even if the affected nail falls off or is knocked off, the new nail that grows usually is infected with fungus.


You can help to prevent toenail fungus by:

  • Wearing comfortable shoes and hosiery that allow your feet some “breathing space”
  • Wearing shoes, sandals or flip-flops in community showers or locker rooms
  • Washing your feet every day, drying them thoroughly and using a good-quality foot powder
  • Wearing clean socks or stockings every day
  • Keeping toenails trimmed
  • Disinfecting pedicure tools before you use them


There are several approaches to therapy. Treatment may begin with your doctor removing as much of the infected nail as possible. This can be done by trimming the nail with clippers, filing it down or dissolving it away with a paste that contains urea and bifonazole.

Next, if the infection is mild and very localized, your doctor may prescribe a medicated nail polish containing either amorolfine (Loceryl) or ciclopirox (Loprox). You should apply the nail polish twice a week until your nail is cured.

If the infection involves a wider area of your nail, or several nails, your doctor will prescribe an oral antifungal medication, such as itraconazole (Sporanox) or terbinafine (Lamisil). Either itraconazole or terbinafine can be taken daily for 12 weeks, or a higher dose of itraconazole can be taken for one week per month for three months. Both itraconazole and terbinafine occasionally cause troublesome side effects, and itraconazole has the potential to produce serious drug interactions in people taking terfenadine (Seldane), astemizole (Hismanal), cisapride (Propulsid), midazolam (Versed), triazolam (Halcion) or lovastatin (Mevacor).

In very severe cases of toenail fungus resistant to therapy, it may be necessary to remove the nail surgically.

When To Call A Professional

You may wish to make an appointment to see your family doctor or podiatrist if you notice that a portion of your toenail has become abnormally thick or discolored. Call your doctor promptly if any problem involving your feet or toes makes walking painful or difficult.


According to one study involving 195 patients with toenail fungus, 81 percent of those treated with terbinafine and 63 percent of those treated with itraconazole were cured fungus after 12 weeks of therapy. However, even after the fungus was dead in these patients, only 36 percent to 50 percent had completely clear, normal-looking nails.

After treatment with itraconazole, the fungus returns after nine to 12 months in 9 percent to 11 percent of patients. After treatment with terbinafine, the fungus returns within 12 months in about 12 percent of patients.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.