Ingrown toenails occur when the corner or side of a toenail grows into the soft flesh, causing pain, inflammation, swelling, and sometimes infection. The most common causes of ingrown toenails include wearing shoes that crowd the toenails, cutting toenails too short or not straight across, injuring a toenail, having very curved toenails, nail infections, and certain medical conditions. Other factors that increase the risk of ingrown toenails include being an adolescent, having nail care habits that encourage the nail to grow into the skin, such as peeling off the edge or trimming down at the corners, and having deformed or misshaped toenails. In rare, chronic cases, an ingrown toenail infection can spread through the toe and into the bone. Mild ingrown toenails can be treated at home by soaking the foot in warm water, placing a twist of cotton under the corner of the nail, and wearing open-toe shoes that do not rub the toenail. If the pain is severe or spreading, or if there is pus or inflamed skin that seems to be spreading, it is recommended to see a healthcare provider. In some cases, surgery may be required to remove the part of the nail that is ingrown.