Ingrown toenail (onychocryptosis) develops when a sharp corner of the toenail digs into the skin at the end of or side of the toe. Pain and inflammation at the spot where the nail curls into the skin occurs first. Later, the inflamed area can begin to grow extra tissue or drain yellowish fluid. Untreated, an ingrown toenail may develop an infection or even an abscess. Osteomyelitis is a rare complication of an infected toe, in which the bone itself becomes infected. Ingrown toenails are common in adults and adolescents. Any toenail can become ingrown, but the condition is most commonly seen in the big toe.