Definition: An ingrown toenail is a toenail that pushes against the skin along the sides of the toe. Sometimes, the nail grows into the skin, or sometimes the skin can grow over the edge of the nail. In either event, the area becomes swollen and painful.
Solution: If it becomes red, this is a sign that you should see a doctor.
Prevention: When you cut your toenails, be sure to cut them straight across (but not too short).