An infection of nail fungus occurs when fungi infect one or more of your nails. A nail fungal infection may begin as a white or yellow spot under the tip of your fingernail or toenail. As the nail fungus spreads deeper into your nail, it may cause your nail to discolor, thicken and develop crumbling edges — an unsightly and potentially painful problem.
These infections usually develop on nails continually exposed to warm, moist environments, such as sweaty shoes or shower floors. Nail fungus isn't the same as athlete's foot, which primarily affects the skin of the feet, but at times the two may coexist and can be caused by the same type of fungus.
An infection with nail fungus may be difficult to treat, and infections may recur. But medications are available to help clear up nail fungus.