(HealthDay News) -- Canker sores are painful ulcers that occur in the mouth. They may be yellow or white in appearance, while the surrounding tissue usually is red.
The U.S. National Library of Medicine mentions these possible causes of canker sores:
If you have a canker sore, avoid hot or spicy foods and try rinsing with salt water. Over-the-counter medicines for mouth sores may also offer some relief.