Nail fungus is a common infection of the nail. It begins as a white or yellow-brown spot under the tip of your fingernail or toenail. As the fungal infection goes deeper, the nail may discolor, thicken and crumble at the edge. Nail fungus can affect several nails.

If your condition is mild and not bothering you, you may not need treatment. If your nail fungus is painful and has caused thickened nails, self-care steps and medications may help. But even if treatment is successful, nail fungus often comes back.

Nail fungus is also called onychomycosis (on-ih-koh-my-KOH-sis). When fungus infects the areas between your toes and the skin of your feet, it’s called athlete’s foot (tinea pedis).

Symptoms of nail fungus include a nail or nails that are:

Nail fungus can affect fingernails, but it’s more common in toenails.

When to see a doctor

You may want to see a health care provider if self-care steps haven’t helped and the nail becomes increasingly discolored, thickened or misshapen. Also talk with your health care provider if you have:

Nail fungus is caused by various fungal organisms (fungi). The most common is a type called dermatophyte. Yeast, bacteria and molds also can cause nail infections. The discoloration from a bacterial infection tends to be green or black.

Fungal infection of the foot (athlete’s foot) can spread to the nail, and a fungal infection of the nail can spread to the foot. You can also get the infection from contact with spaces where fungi can thrive, such as the floor tile in a gym shower or inside dark, sweaty, moist shoes.

Factors that can increase your risk of developing nail fungus include:

A severe case of nail fungus can be painful and may cause permanent damage to your nails. And it may lead to other serious infections that spread beyond your feet if you have a suppressed immune system due to medication, diabetes or other conditions.

The following habits can help prevent nail fungus or reinfections and athlete’s foot, which can lead to nail fungus:

Your health care provider will examine your nails and perhaps take some nail clippings or scrape debris from under your nail. These samples are sent to a lab to identify the cause of your symptoms.

Other conditions, such as psoriasis, can mimic a fungal infection of the nail. Microorganisms such as yeast and bacteria also can infect nails. Knowing the cause of your infection helps determine the best treatment.

Treatment for toenail fungus isn’t always needed. And sometimes self-care and nonprescription products clear up the infection. Talk with your health care provider if your condition doesn’t improve. Treatment depends on the severity of your condition and the type of fungus causing it. It can take months to see results. And even if your nail condition improves, repeat infections are common.

Medications

Your health care provider may prescribe antifungal drugs that you take by mouth (orally) or apply to the nail.

Surgery

Your health care provider might suggest temporary removal of the nail so that the antifungal drug can be applied directly to the infection under the nail.

The most effective but least used option is surgery to permanently remove the nail and its root.

Often, you can take care of a fungal nail infection at home:

Before trimming or using a nail file to thin thick nails, soften them with urea-containing creams. See a health care provider for foot care if you have a condition that causes poor blood flow to your feet.

You’re likely to start by seeing your primary care provider. In some cases when you call to set up an appointment, you may be referred immediately to either a doctor who specializes in skin conditions (dermatologist) or one who specializes in foot conditions (podiatrist).

Here are some steps you can take to prepare for your appointment:

For nail fungus, your questions might include:

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