Candida is the genus name for a number of bacterial yeasts. The most common variety is Candida albicans. It lives in the small intestine and the mucous membranes, where it generally doesn't cause any trouble because it is kept in check by the “friendly bacteria” that live there, too. But if the balance is upset, Candida can thrive and start to cause problems, including infections on the fingernails and toenails.

While nail infections are common enough -- about 7 percent of adults suffer from them, usually in the toenails as opposed to the fingernails -- the leading cause is not Candida but fungi from the genus Trichophyton. Those fungi are responsible for the vast majority of nail infections. Still, Candida is sometimes to blame. Whatever the specific cause, if a fungus invade the nails, it is known as onychomycosis

Studies show that men are twice as likely to suffer from nail infections than women are, and that the likelihood increases with age. Also, those with compromised immune systems (as with HIV) are particularly susceptible to it.

In the most common kind of nail infection, distal subungual onychomycosis (DSC), the fungus enters between the tip of the nail and the toe (or finger, but rarely) and causes the nail plate to separate from the skin underneath it. The nail also turns white, green, or yellow.

There is usually no pain at first, but the nail is ugly, and people suffering from onychomycosis are often embarrassed to let others see it and may avoid social situations where it would be visible. Because of that, while the infection may not be painful or medically dangerous, treating it is more than merely a cosmetic consideration. Psychologically, no one wants to have something dead and ugly attached to their bodies.

As the fungus progresses, the nail becomes thick and hard and separates farther from the toe. Also, dead, dry material collects between the nail and the nail bed. Sometimes it becomes painful, though often, if the nail is thick enough, the pain is negligible or absent altogether.

The most effective treatments for nail infections, whether candida-induced or otherwise, are basic systemic antifungal medications. Slightly less effective are topical treatments (ointments or creams that go directly on the affected area), though better ones are being developed.

There are folk remedies, too, that some people swear by while others scoff. Tea tree oil is a known antifungal that, when applied topically to the nail itself, is generally effective. (It's one of the few “home remedies” that medical science can back up.) Grapefruit seed extract is also used, but its effectiveness has not been confirmed. Likewise, applying vinegar to the cuticle, a few drops a day for several weeks, may be helpful in some patients.

In general, the home remedies get the basic idea right: Pay attention to your nails! It is so much easier to prevent the condition than to treat it. Keep your feet clean and dry, don't wear tight or moist socks or shoes, and keep your nails trimmed and clean.