The most common symptoms of fungal nails are the thickening and/or discoloration of the nail (white, black, yellow or green). The nail may become brittle and crumble around the edges, or even break off from the toe (or finger) completely. If left untreated, the infection can become painful. The skin may also become inflamed and painful underneath and around the nail. Possible treatments include topical medication, oral medication, surgery, and laser.