Technically called “onychomycosis”, fungal infection of the nail plate (the hard outer nail) or nail bed (that lies under the hard nail) will most often appear as yellowish, white, black or green discolouration of the nail. The infected nail may also appear thickened or brittle. In severe cases, from long-term infection (where all the tissues of the nail have been infected), the infected nail may break up and fall off.
Removal of the nail can reduce symptoms rapidly, but regrowth of the nail can take one year during which time local treatment for fungus can be used. Oral medications include terbinafine (Lamisil), itraconazole (Sporanox), and griseofulvin (Fulvicin). Treatment regimens vary and can last between six weeks and one year. Side effects of systemic treatment include gastrointestinal disorders, liver toxicity, skin rash and other hypersensitivities. These medications should not be taken during pregnancy or if there is a chance you will become pregnant because of effects on the fetus.
Use soap and water to wash your feet, and dry well, including between toes. Trim your toenails -- straight across -- to keep them shorter than the end of your toe. Make sure the tools you use are clean, too. Wash clippers and files with soap and water, then wipe with rubbing alcohol. You might be tempted to cover up discolored nails with polish, but don't. Your nail bed can't "breathe," which keeps fungus from going away.