Nails whose corners or sides dig painfully into skin, often causing infection. Can be caused by improper nail trimming, pressure from shoes that are too small, injury, fungus infection, heredity, and poor foot structure. Trim toenails straight across to prevent problems. Soak the foot in soapy water, apply antiseptic, and bandage. Wear well-fitting shoes. If a toenail is painful or infected, the doctor may remove the ingrown portion.