A fungal nail infection occurs when a fungus attacks a fingernail, a toenail, or the skin under the nail, called the nail bed. Fungi (plural of fungus) can attack your nails through small cuts in the skin around your nail or through the opening between your nail and nail bed.

Fungal nail infections are more common in toenails than fingernails. Toenails grow very slowly, giving the fungi more time to develop and get worse. It also takes more time to treat toenails than fingernails.

Yeasts, molds, and different kinds of fungi can cause fungal nail infections. Most are caused by the same type of fungus that causes athlete's foot. Fungi grow best in warm, moist places, and they can spread from person to person. You can get a fungal nail infection from walking barefoot in public showers or pools or from sharing personal items, such as towels and nail clippers. If you have athlete's foot, the fungus can spread from your skin to your nails.

You might use antifungal pills if topical treatments have not worked. A fungal nail infection doesn't go away on its own. And it slowly gets worse over time. An infection may spread into the nail root, where new nail growth begins, and may spread to other nails. The longer you have an infection and the worse it gets, the harder it is to treat.

Severe infections, especially in older people who have had the condition for many years, can cause very thick nails that are hard to trim. They may cause pain or discomfort when you walk. If this happens, it is hard to cure a fungal infection, even with antifungal pills.

Not all fungal nail infections need treatment with pills. Some people decide not to treat a fungal infection until it is uncomfortable or painful.

Nail infections are hard to treat, and antifungal pills can be costly. There is no guarantee that the pills will work or that the infection won't come back.

The pills used to treat fungal nail infections can cause side effects, including stomach problems and headaches. In rare cases, some of these medicines may cause liver damage and heart failure.

You might think about trying other treatments, such as using an antifungal cream, having laser treatment, or having your nail removed.

Pills to treat fungal nail infections include terbinafine (Lamisil) and medicines called azoles, such as itraconazole (Sporanox) and fluconazole (Diflucan). Studies looking at antifungal medicines found that:^{footnote 1}

• Terbinafine seems to work a little better than azole medicines.
• Terbinafine and azole medicines have about the same rate of side effects.
• The chance of an infection returning is about the same with terbinafine or with azole medicines.

Another antifungal medicine that is used less often is griseofulvin. It seems to work about as well as azole medicines, but griseofulvin causes more side effects.^{footnote 1}

If you are healthy, an ongoing fungal nail infection has no serious risks. But over time, the nail may get thick and look bad. It may be painful when you wear shoes or walk.

If you have diabetes or a weak immune system, a fungal infection can lead to a more serious bacterial infection.

Your doctor may advise you to use pills if:

• You have a painful nail infection.
• You have another health problem, such as diabetes, that can cause problems from foot infection.