Canker sores (aphthous ulcers) usually come from a mix of triggers rather than one single cause, and in many people the exact reason stays partly mysterious.

What canker sores are

  • Small, shallow ulcers that form on the soft tissue inside the mouth (cheeks, tongue, inner lips, soft palate, gum lining), not on the outer lip like cold sores.
  • Typically round or oval with a white, yellow, or gray center and a red, inflamed border, and they often sting when eating, drinking, or brushing.

Why we get canker sores

Researchers think canker sores happen when the immune system overreacts to triggers in the lining of the mouth, especially in people who are genetically predisposed.

Common contributing factors include:

  • Minor trauma
    • Biting your cheek or tongue
    • Braces, sharp teeth, illā€‘fitting dentures
    • Vigorous brushing or rough dental work
  • Immune and genetic factors
    • Family tendency to get frequent canker sores
    • Immune system ā€œattackingā€ cells of the mouth lining by mistake
  • Deficiencies and nutrition
    • Low vitamin B12, folate, iron, or zinc levels
    • Poor general nutrition or restrictive diets
  • Stress and hormones
    • Emotional stress or lack of sleep
    • Hormonal changes (for example around menstruation)
  • Foods and chemicals
    • Very acidic or spicy foods (citrus, tomatoes, vinegar, hot sauces)
    • Possible sensitivity to certain ingredients like sodium lauryl sulfate in some toothpastes
  • Medical conditions (in some people)
    • Celiac disease, inflammatory bowel disease, BehƧet disease, ironā€‘deficiency anemia, and immuneā€‘compromising conditions are linked with more frequent or severe canker sores.

Why some people get them more

  • Some people inherit a tendency: if close family members get recurrent canker sores, your own risk is higher.
  • When several triggers pile up at once (for example stress + mouth bite + low B12), a sore is more likely to appear and may take longer to heal.

When to worry and see a doctor

Most canker sores are harmless and heal within 1ā€“2 weeks, but you should get checked if:

  • A sore is extremely large, very painful, or lasts longer than about 2ā€“3 weeks.
  • You keep getting many sores at once or they come back constantly.
  • You have sores plus other symptoms like fever, weight loss, diarrhea, eye or genital sores, or severe fatigue.

These situations can be a sign of an underlying condition or a different kind of mouth lesion that needs specific treatment.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.