They usually heal within 2 weeks, but they often come back. Causes The cause of canker sores is unknown. The sores are small, painful, gray-colored spots that are circled in red. For 2 or 3 days, you may experience pain when you eat or speak. There is no cure for canker sores.
Some medicines can ease the pain.
Follow your doctor's advice for caring for your mouth. You may need to have your dentures or braces adjusted if they are causing the sores. Medicines and lozenges to numb and protect the sores. Follow the directions on the label. Milk of magnesia.