An infection of nail fungus develops when fungi infect one or more of the nails. A nail fungal infection may begin as a white or yellow spot under the tip of the fingernail or toenail. As the nail fungus spreads deeper into the nail, it may result to nail discoloration, thickening and developing of crumbling edges — an unsightly and potentially painful problem.

The doctor will likely examine the patient's nails first. To test for fungi, the doctor may scrape some debris from under the nail for analysis.

To treat nail fungus, the doctor may prescribe an oral antifungal medication, such as: Itraconazole (Sporanox); Fluconazole (Diflucan); and Terbinafine (Lamisil).

The infected nails may be thickened; brittle, crumbly or ragged; distorted in shape; dull, with no luster or shine; dark color, caused by debris building up under the nail. Infected nails may also separate from the nail bed, a condition known as onycholysis. The patient may even feel pain in the toes or fingertips and detect a slightly foul odor.

Fungi are microscopic organisms that don't require sunlight to survive. Some fungi have beneficial uses, while others lead to illness and infection. Nail fungal infections are usually caused by a fungus that belongs to a group of fungi called dermatophytes. But yeasts and molds also can be the cause of nail fungal infections.