Canker sores are small ulcers inside the mouth, and the exact cause is often unknown, but they’re commonly linked to mouth injury, stress, certain foods, vitamin or mineral deficiencies, hormonal changes, and sometimes family history. They are not the same as cold sores and are not contagious.

Common triggers

  • Biting the inside of your cheek or tongue.
  • Brushing too hard, dental work, braces, or dentures.
  • Stress or fatigue.
  • Acidic or spicy foods, and sometimes toothpaste ingredients.
  • Low levels of iron, folate, vitamin B12, or zinc.
  • Hormonal shifts, especially around periods.

When to get checked

Most canker sores heal on their own within about 1 to 2 weeks. If sores are large, very frequent, or do not heal, that can point to another issue and should be evaluated.

What helps

  • Rinse with warm salt water.
  • Use a soft toothbrush.
  • Avoid spicy, acidic, or very hot foods.
  • Consider an over-the-counter numbing gel for pain relief.
Quick Scoop: Canker sores usually happen because the mouth lining gets irritated or because of an underlying trigger like stress, injury, or a nutrient deficiency, but the exact reason often isn’t clear.[2][4]