Ingrown Toenail Treatment - Podiatrist in Annapolis, MDDr. James McKee discusses the symptoms, causes and treatment for ingrown toenails. toenails, also known as onychocryptosis, is usually caused by trimming toenails too short, particularly on the sides of the big toes. They may also be caused by shoe pressure (from shoes that are too tight or short), injury, fungus infection, heredity, or poor foot structure. Ingrown toenails occur when the corners or sides of the toenail dig into the skin, often causing infection. A common ailment, ingrown toenails can be painful. Ingrown toenails start out hard, swollen, and tender. Left untreated, they may become sore, red, and infected and the skin may start to grow over the ingrown toenail.