Mouth ulcers (canker sores) usually come from a mix of irritation, triggers, and sometimes underlying health issues, especially if you “keep” getting them repeatedly.

Common everyday triggers

These are the simple, day‑to‑day reasons many people get recurring mouth ulcers.

  • Minor trauma: Biting your cheek or tongue, sharp or broken teeth, braces, dentures, or rough fillings rubbing the lining of your mouth.
  • Toothbrushing injuries: Brushing too hard or using a hard‑bristled brush that scrapes the gums or cheeks.
  • Hot or rough foods: Very hot drinks, toasted bread, crisps/chips, or other rough foods that scratch or burn the inside of the mouth.
  • Irritating toothpaste or mouthwash: Products containing sodium lauryl sulfate (SLS) can trigger ulcers in some people.

Example

If you often get an ulcer in the same spot where a tooth edge or brace wire rubs, that repeated friction is a likely cause.

Lifestyle and body factors

Your overall health and habits can make you more prone to frequent ulcers.

  • Stress and fatigue: Emotional stress and being run‑down are major triggers; they can weaken your immune response and make ulcers flare up more often.
  • Hormonal changes: Some people, especially women, notice ulcers around menstruation, pregnancy, or other hormonal shifts.
  • Diet and food triggers: Citrus fruits, spicy foods, chocolate, coffee, strawberries, nuts, and sometimes gluten can provoke ulcers in sensitive people.
  • Nutrient deficiencies: Low vitamin B12, iron, folate, or zinc are strongly linked with recurrent mouth ulcers.

Medical and medication causes

If ulcers are very frequent, severe, or slow to heal, there may be an underlying medical reason.

  • Gut and immune conditions:
    • Coeliac disease (gluten sensitivity)
    • Inflammatory bowel disease (like Crohn’s)
    • Behçet’s disease
    • Other immune problems including HIV/AIDS
  • Blood disorders: Anaemia or other blood problems can present with repeated mouth ulcers.
  • Infections: Viral illnesses (like herpes) and some other infections can cause ulcer‑type sores.
  • Medicines and treatments: Some medications and treatments (for example certain painkillers, chemotherapy, or immune‑affecting drugs) list mouth ulcers as a possible side effect.

When to worry and see a doctor or dentist

Frequent ulcers can usually be improved, but there are times you should get checked.

Go to a doctor or dentist if:

  • An ulcer lasts longer than 2–3 weeks or keeps coming back in exactly the same spot.
  • Ulcers are unusually large, very painful, or come in clusters again and again.
  • You also have weight loss, persistent diarrhoea or tummy pain, fevers, night sweats, or feel very tired and unwell.
  • You notice hard lumps, non‑healing patches, or colour changes in your mouth (this needs urgent assessment to rule out more serious causes).

What you can do next

You can often reduce how often you get mouth ulcers by changing a few things.

  • Protect your mouth: Ask your dentist to smooth sharp teeth or brace wires; fix ill‑fitting dentures.
  • Gentler oral care: Use a soft toothbrush and consider an SLS‑free toothpaste if you suspect irritation.
  • Track triggers: Keep a simple diary of foods, stress, sleep, and when ulcers appear to spot patterns.
  • Check your nutrition: Ask your clinician about tests for iron, B12, folate, and other deficiencies if you get frequent ulcers.
  • Manage stress: Relaxation, better sleep, and stress‑management strategies can reduce flare‑ups for many people.

Important: I can’t tell you exactly why you keep getting mouth ulcers or give a diagnosis.
If your ulcers are frequent, severe, or not healing, please see a doctor or dentist for an in‑person assessment and appropriate tests.

TL;DR:
You may keep getting mouth ulcers because of repeated minor injuries, stress, certain foods or toothpaste, vitamin deficiencies, or less commonly underlying conditions like coeliac disease or blood problems; getting checked is a good idea if they’re frequent, very painful, or slow to heal.

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