Nail fungus is a fungal infection in one or more of your nails. An infection with nail fungus 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.
An infection with nail fungus may be difficult to treat, and it may recur. But medications are available to help clear up nail fungus.