Last updated: October 2026
Mouth ulcers are small, painful sores inside the mouth, usually on the cheeks, lips or tongue. Most are caused by biting your cheek, a sharp tooth, stress, tiredness or hormonal changes. The NHS says they should clear up on their own within a week or 2. See a dentist or GP if one lasts longer than 3 weeks.
Below: the common causes, a quick guide to the types, what helps and when to get one checked.
What is a mouth ulcer?
A mouth ulcer is a small break in the soft lining of your mouth. They’re usually round or oval, can look white, red, yellow or grey, and appear on the inside of the cheeks or lips, or on the tongue. You can have more than one at a time.
Mouth ulcers are not contagious. They’re also different from cold sores, which appear on the lips or around the mouth and often start with a tingling, itching or burning feeling.
Doctors call the common, recurring kind aphthous ulcers (recurrent aphthous stomatitis).
What causes mouth ulcers?
The NHS says most single mouth ulcers are caused by things you can try to avoid.
Damage to the inside of your mouth
- Biting the inside of your cheek or lip.
- A sharp tooth, rough filling, braces or badly fitting dentures rubbing the same spot.
- Cuts or burns from food and drink, such as hard, crunchy food or a very hot drink.
- Damaging your gums with your toothbrush, or an irritating toothpaste.
Triggers for ulcers that keep returning
- Feeling tired, stressed or anxious. See stress symptoms.
- Hormonal changes, for example during pregnancy, and some women get mouth ulcers during their period. See hormonal imbalance symptoms.
- Certain foods. NHS inform lists chocolate, spicy foods, coffee, peanuts, almonds, strawberries, cheese, tomatoes and wheat flour as possible triggers.
- Toothpaste containing sodium lauryl sulphate (SLS), a foaming agent. More on the evidence below.
- Stopping smoking. Some people get mouth ulcers when they first quit.
- Your genes. Around 40% of people who keep getting mouth ulcers say it runs in their family.
Low vitamins, medical conditions and medicines
- Low iron, vitamin B12 or folate. The NHS also mentions zinc and vitamin D. See vitamin B12 deficiency symptoms, iron deficiency symptoms and our guide to zinc.
- Digestive conditions such as coeliac disease and Crohn’s disease.
- Viral infections such as hand, foot and mouth disease, and conditions that weaken the immune system.
- Some medicines, including NSAID painkillers such as ibuprofen, beta blockers and nicorandil. Don’t stop a prescribed medicine without speaking to your GP or pharmacist.
Types of mouth ulcer: quick guide
A rough guide to help you describe what you’ve got to a pharmacist, dentist or GP, not a way to diagnose yourself.
| Type | How it looks | Likely cause | What to do |
|---|---|---|---|
| Injury (traumatic) ulcer | A single sore where you bit your cheek or something rubs | Bite, sharp tooth, brace, denture or burn | Self-care; see a dentist about a sharp tooth or loose denture |
| Minor aphthous ulcer (the most common) | Small, round, clearly defined and painful | Often unclear; stress, hormones, foods or SLS can trigger it | Self-care or pharmacy; usually heals in 10 to 14 days without a scar |
| Major aphthous ulcer | Larger (over 5mm) | As above | Can last 6 weeks or longer and may scar: see a dentist or GP |
| Herpetiform ulcers | Clusters of pinpoint sores that can merge into larger, irregular ulcers | As above | Usually last 7 to 10 days; ask a pharmacist |
| Several ulcers plus other symptoms | With a rash on the hands and feet, a white lacy pattern inside the cheeks, or gut symptoms | Hand, foot and mouth disease, oral lichen planus, Crohn’s or coeliac disease | See a GP |
| Ulcer that won’t heal, or a red or white patch | Lasts more than 3 weeks, or looks different from your usual ulcers | Usually harmless, but sometimes a sign of mouth cancer | Book a dentist or GP appointment |
Hand, foot and mouth disease is common in children but can affect adults. It often starts with a high temperature and a sore throat, and usually clears in 7 to 10 days.
Can stress cause mouth ulcers?
It can. The NHS lists feeling tired, stressed or anxious among the causes of mouth ulcers, and NHS inform includes stress and anxiety among the triggers for ulcers that keep coming back.
NHS inform also lists reducing stress and anxiety as part of self-care. See how to relieve stress, sleep deprivation and our bedtime routine for adults.
If a warm evening drink is part of your wind-down, our Magnesium Glycinate Sleep Complex is a caffeine-free berry drink. Magnesium contributes to normal psychological function and to the normal functioning of the nervous system. It isn’t a treatment for mouth ulcers. It’s for adults only, and we don’t recommend our products during pregnancy or breastfeeding.
How long do mouth ulcers last?
Most mouth ulcers clear up by themselves within 1 to 2 weeks. The common small kind usually heals in 10 to 14 days without leaving a scar. Larger ulcers can take longer, sometimes several weeks.
The NHS says there’s no quick fix, but you can make them less painful. If an ulcer lasts longer than 3 weeks, get it checked by a dentist or GP.
How to get rid of mouth ulcers: what helps
Avoiding things that irritate an ulcer can help it heal faster, reduce pain and make it less likely to come back.
Do
- Use a soft-bristled toothbrush.
- Drink cool drinks through a straw.
- Eat softer foods.
- Keep up regular dental check-ups.
- Eat a healthy, balanced diet.
Don’t
- Eat very spicy, salty or acidic food.
- Eat rough, crunchy food such as toast or crisps.
- Drink very hot or acidic drinks, such as fruit juice. See our vitamin C guide for other sources.
- Chew gum.
- Use toothpaste containing sodium lauryl sulphate.
Salt water rinse
Dissolve half a teaspoon of salt in a glass of warm water, rinse, then spit it out (don’t swallow it). Repeat as often as you like.
From a pharmacy
A pharmacist can recommend something to speed up healing, prevent infection or reduce pain, without a prescription. Options include:
- an antimicrobial mouthwash
- a painkilling tablet, mouthwash, gel or spray
- corticosteroid lozenges
- a salt (saline) mouthwash
Tell the pharmacist about any medicines you take, or if you’re pregnant or buying for a child.
From a dentist or GP
For severe, persistent or infected ulcers, a dentist or GP may prescribe stronger treatment, such as a steroid spray or dissolving tablets.
Does toothpaste cause mouth ulcers?
Possibly, for some people. Many toothpastes contain sodium lauryl sulphate (SLS), the ingredient that makes them foam, and both the NHS and NHS inform advise avoiding it if you get mouth ulcers.
The research is small but points the same way. A 2019 systematic review found 4 double-blind trials with 124 people who get recurrent ulcers. Compared with SLS toothpaste, SLS-free toothpaste reduced the number of ulcers, how long they lasted, how often they came back and how much they hurt, although the authors said better trials are still needed. In one 2012 trial of 90 people, SLS-free toothpaste didn’t cut the number of ulcers, but they healed faster and hurt less.
If you keep getting ulcers, it’s an easy thing to try: check the ingredients and switch to an SLS-free toothpaste for a couple of months.
Mouth ulcers that keep coming back
An occasional mouth ulcer is common. If you keep getting them, see a dentist or GP, as there may be a cause that can be treated. A GP may look for:
- Low iron, vitamin B12 or folate, checked with a blood test. A 2015 analysis of 9 studies found low levels were more common in people with recurrent ulcers. The NHS lists a sore or red tongue, sometimes with ulcers, as a symptom of B12 or folate deficiency anaemia. See why am I always tired?
- Coeliac disease. The NHS says you should be tested if you have severe or persistent mouth ulcers. Testing starts with a blood test, and you need to keep eating gluten until it’s done. See our gut health guide.
- Crohn’s disease or other conditions, and your medicines.
What about vitamin B12 for mouth ulcers?
In a small 2009 trial, 58 people with recurrent ulcers took either 1,000mcg of vitamin B12 under the tongue or a placebo for 6 months. The B12 group had shorter outbreaks, fewer ulcers and less pain, whatever their starting B12 level, and in the final month 74% had no ulcers compared with 32% on placebo. It’s one small study. A larger 2012 trial gave 160 adults a standard daily multivitamin or a placebo for up to a year and found no difference.
So the honest answer is: get a blood test first, and ask your GP or pharmacist before taking high-dose B12. If you are low in iron, see iron-rich foods alongside any treatment your GP recommends. For reference, vitamin B12 contributes to normal red blood cell formation, and iron contributes to normal formation of red blood cells and haemoglobin. Evopure doesn’t sell iron, B12 or folate supplements.
When to see a dentist or GP
See a dentist or GP if your mouth ulcer:
- lasts longer than 3 weeks
- keeps coming back
- is different from ulcers you’ve had before, for example bigger than usual or near the back of your throat
- bleeds, or becomes more painful and red, which may be a sign of infection
Also see a GP if you have ulcers anywhere else on your body, such as your skin or genitals, or painful, red or swollen joints.
Mouth ulcers and mouth cancer
Most mouth ulcers are harmless. But the NHS says a mouth ulcer that lasts more than 3 weeks can sometimes be a sign of mouth cancer, so it’s best to get it checked. Also get checked for a red or white patch in your mouth, a lump in your mouth, lip or neck, mouth pain that isn’t going away, difficulty swallowing or speaking, or a hoarse voice that won’t go away. These symptoms are common and can have other causes, but finding cancer early can make it easier to treat, and regular dental check-ups help spot early signs.
If the sore is on the outside of your lip, it’s more likely a cold sore: see our guide to cold sores.
FAQs
Can stress cause mouth ulcers?
Yes, it’s a common trigger. The NHS lists feeling tired, stressed or anxious among the causes of mouth ulcers.
What vitamin deficiency causes mouth ulcers?
Low iron, vitamin B12 and folate are the best known. The NHS also mentions zinc and vitamin D. If you keep getting ulcers, ask your GP about a blood test.
How do you get rid of a mouth ulcer fast?
There’s no quick fix, and most heal in 1 to 2 weeks. Avoid spicy, acidic and crunchy food, use a soft toothbrush, rinse with salt water and ask a pharmacist about a gel, spray or mouthwash.
Are mouth ulcers contagious?
No. Mouth ulcers are not contagious. Cold sores are different: they appear on the lips or around the mouth and often start with tingling or burning.
When should I worry about a mouth ulcer?
See a dentist or GP if an ulcer lasts longer than 3 weeks, keeps coming back, is bigger than usual, bleeds or gets more painful and red, or if you notice a red or white patch or a lump in your mouth.
Sources
- NHS. Mouth ulcers.
- NHS inform. Mouth ulcer.
- NHS. Symptoms of mouth cancer.
- NHS. Coeliac disease: diagnosis.
- Alli BY et al. Effect of sodium lauryl sulfate on recurrent aphthous stomatitis: a systematic review. J Oral Pathol Med, 2019.
- Volkov I et al. Effectiveness of vitamin B12 in treating recurrent aphthous stomatitis: a randomized, double-blind, placebo-controlled trial. J Am Board Fam Med, 2009.
- Lalla RV et al. Multivitamin therapy for recurrent aphthous stomatitis: a randomized, double-masked, placebo-controlled trial. J Am Dent Assoc, 2012.
- Chen H et al. Impact of haematologic deficiencies on recurrent aphthous ulceration: a meta-analysis. Br Dent J, 2015.
- Ship JA. Recurrent aphthous stomatitis: an update. Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 1996.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex mentioned above.
