What is toenail fungus and what's the best way to get rid of it?

Toenail fungus, or onychomycosis, is common, affecting 3 percent to 5 percent of Americans. It can start with simple athlete's foot, a fungal infection that if untreated can lead to infection deep into the nail matrix, from which the nail grows.

The microorganism that causes toenail fungus is a dermatophyte, which lives on keratin, the protein that nails are made of, and thrives in the dark, moist, warm environment of sweaty feet.

As toenail fungi grow, the nails become thicker and may smell foul. The thickened nails can then press into the nail bed, causing pain, especially in tight shoes.

Topical prescription solutions such as Loprox, Loceryl, Keralac, and Penlac may help, said Dr. Peter Paicos Jr. , immediate past president of the Massachusetts Podiatric Medical Society and associate medical director of the wound healing center at Winchester Hospital. There are also some nonprescription topical solutions available, including Mycocide NS.

If topical treatments don't work, you can try oral medications such as Lamisil or Sporanox, which are usually taken daily for 12 weeks. But the oral medications can in rare cases cause liver damage , so you should get a liver function test before starting these medications and during the course of treatment, said Dr. Joseph Caporusso , a McAllen, Texas, podiatrist and trustee of the American Podiatric Medical Association.

In really stubborn cases, the permanent solution is to remove the infected nail and nail root surgically.

To prevent toenail fungus in the first place, wear comfortable shoes that allow your feet some breathing room, wear sandals in public locker rooms, wash your feet every day, and wear clean socks or stockings every day.

JUDY FOREMAN

E-mail health questions to Foreman@globe.com.