Nail fungus is a common nail condition that begins as a white or yellow spot under the tip of a fingernail or toenail. As the fungal infection goes deeper, nail fungus may cause nails to discolor, thicken and crumble at the edge. It can affect several nails.

Other conditions, such as psoriasis, can mimic a fungal infection of the nail. Microorganisms such as yeast and bacteria also can infect nails. Knowing the cause of your infection helps determine the best course of treatment - topical or oral medications can be used.