Canker Sores: what it usually means
Also searched as: aphthous ulcers, mouth ulcers, oral ulcers · Updated 19 Aug 2026 · Educational — not medical advice
The short answer: Canker sores are small, shallow ulcers inside the mouth — on the cheeks, lips, or tongue — that are not contagious and usually heal within one to two weeks. They are commonly triggered by minor mouth injury, stress, certain foods, or nutrient deficiencies such as low vitamin B12, folate, or iron. Sores that are unusually large, extremely painful, or keep recurring frequently deserve a closer look to rule out an underlying deficiency or condition.
See a doctor promptly if…
Sores larger than usual, unusually painful, or lasting longer than two to three weeks.
Canker sores recurring frequently, more than a few times a year.
Sores accompanied by fever, tiredness, or swollen lymph nodes.
Difficulty eating or drinking because of pain.
Sores appearing alongside other symptoms like digestive changes or unexplained weight loss.
Common causes
- Minor mouth injury — Accidental bites, braces, or a rough toothbrush can trigger a small ulcer at the site of irritation.
- Stress — Periods of high stress are commonly linked to more frequent canker sore outbreaks.
- Certain foods — Acidic fruits, spicy foods, or foods you're sensitive to can trigger or worsen sores in some people.
- Nutrient deficiencies — Low vitamin B12, folate, or iron are recognized contributors to recurrent canker sores in some people.
- Hormonal changes — Some people notice sores appearing around their menstrual cycle.
- Underlying digestive or immune conditions — Conditions like celiac disease or inflammatory bowel disease can cause recurrent mouth ulcers as one of their signs.
What helps
- Rinse with warm salt water a few times a day to ease discomfort and support healing.
- Avoid acidic, spicy, or rough-textured foods while the sore heals.
- Use an over-the-counter oral gel or paste to reduce pain during eating.
- Use a soft-bristled toothbrush to avoid further irritating the area.
Which doctor to consult
A dentist can rule out a local irritant, while a family doctor can check for nutrient deficiencies or an underlying digestive or immune condition if sores are frequent or severe.
Lab tests doctors often check
If this symptom persists, these are the values a doctor commonly looks at — and if you already have a report, the analyzer explains where you stand.
Questions people ask
Are canker sores the same as cold sores?
No — canker sores occur inside the mouth, are not contagious, and are not caused by a virus, while cold sores appear on or around the lips, are caused by the herpes simplex virus, and are contagious. Treatment and precautions differ accordingly, so it helps to know which one you have.
Can a vitamin deficiency really cause mouth ulcers?
Yes — low vitamin B12, folate, or iron are recognized contributors to recurrent canker sores in some people, likely because these nutrients support the rapid cell turnover the mouth's lining depends on. If sores keep recurring, a simple blood test can check for these deficiencies.
Related symptoms
This guide is educational and doesn't replace a clinical assessment. If a symptom is severe, rapidly worsening, or worrying you, see a doctor — being checked and reassured is never a wasted visit.