Mouth ulcers (like canker sores) usually happen when the lining of your mouth gets damaged or irritated and your immune system overreacts while trying to heal it.

What exactly is a mouth ulcer?

  • A mouth ulcer is a small, painful sore on the soft tissues inside your mouth (cheeks, lips, tongue, gums, or palate).
  • The top layer of the lining breaks down, leaving a shallow “crater‑like” area that looks white, yellow, or grey with a red border.
  • They are usually not contagious and most heal on their own in 7–14 days.

Common everyday triggers

  • Minor injuries : Biting your cheek or tongue, sharp teeth, braces, dentures, hard or crunchy foods, or burns from hot drinks/food can injure the lining and start an ulcer.
  • Rough brushing or irritating toothpaste/mouthwash can repeatedly rub or chemically irritate the area.
  • Stress, tiredness, or lack of sleep can lower local immunity and make the lining more fragile, so small injuries turn into ulcers more easily.

Internal body factors

  • Vitamin and mineral deficiencies (especially iron, folate, vitamin B12, zinc, and sometimes vitamin D) are linked with frequent mouth ulcers.
  • Hormonal changes (periods, pregnancy, menopause) can make some people more prone to ulcers at certain times of the month.
  • Genetics also plays a role: in some families, several people get recurrent mouth ulcers even with good habits.

Foods, products, and illnesses

  • Certain foods can trigger or worsen ulcers in some people: citrus fruits, spicy food, chocolate, nuts, coffee, strawberries, or gluten if you are sensitive.
  • Toothpaste with sodium lauryl sulphate (the foaming agent) can trigger canker sores in some people; switching to SLS‑free products helps some patients.
  • Some medical conditions (like coeliac disease, Crohn’s disease, Behçet’s disease, HIV, and other immune or gut problems) can cause frequent or severe ulcers as one of their signs.

Medicines and when to worry

  • Certain medicines (for example, some painkillers like NSAIDs, beta‑blockers, and a heart drug called nicorandil, as well as some cancer treatments) can cause mouth ulcers as a side effect.
  • See a doctor or dentist urgently if: an ulcer lasts longer than 3 weeks, keeps coming back in the same place, is unusually large, you have many at once, or you also have weight loss, fever, skin/genital ulcers, or feel very unwell.

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