Toenail, ingrown: A common disorder, particularly on the big (great) toe, in which the corner of the nail curves down into the skin due to mistrimming of the nail or due to shoes being too tight. An ingrown toenail can be painful and lead to infection. Sometimes simply removing the corner of the nail from the skin is enough to cure this problem, although this might need to be done by a physician, podiatrist, or foot-care specialist. Any infection that is present requires treatment. In some cases the entire nail must be removed. If ingrown toenails are caused by congenital nail malformations, the nail bed can be treated to permanently prevent regrowth.