Ingrown Nail: A nail becomes ingrown when portion of the toenail curves and grows into the flesh of the toe. Many people suffer from ingrown nails. Toenail injury, sports, ill-fitting shoes, and improper nail care are just some of the causes of ingrown nails. Sometimes an ingrown nail can become infected. If this happens, an area of redness, swelling, and drainage may develop along the nail border. Treatment consists of either trimming the ingrown nail, or corrective surgery on the offending nail border.