(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:

  • Problems with the body's immune system.
  • A viral infection.
  • An injury to the mouth, caused by factors such as an accidental biting your tongue or cheek, dental work or a vigorous cleaning.
  • Emotional stress.
  • Insufficient consumption of certain vitamins or minerals.
  • A menstrual period or hormonal changes.
  • Food allergies.

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.