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Mouth ulcers
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In one pass The most common kind of recurring mouth ulcer is called recurrent aphthous stomatitis: a round or oval shallow crater in the lining of the mouth, with a yellow-white or grey floor and a red ring around it.
Educational content, not medical advice — consult a clinician.
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Chapter 1
What a mouth ulcer is
The most common kind of recurring mouth ulcer is called recurrent aphthous stomatitis: a round or oval shallow crater in the lining of the mouth, with a yellow-white or grey floor and a red ring around it. It appears on the inside of the cheeks or lips or on the tongue, and it hurts when touched.
It is not an infection and not contagious, but it should be told apart from cold sores, which are caused by the herpes virus, appear on or around the lips, can also show up inside the mouth as a small group of pinhead-sized ulcers, and are contagious. Most people's ulcers are under 1 cm and heal on their own in 7 to 10 days without a scar; in about one in ten people, ulcers are over 1 cm, can last for weeks and can scar.
They keep coming back because the problem is not some germ in the mouth but the way the lining and the immune system get along: a small irritation, in someone prone to ulcers, is amplified into a local attack.
If an ulcer has not healed after 3 weeks, see a dentist or doctor: most mouth ulcers are harmless, but one that will not heal is occasionally a sign of mouth cancer.
It is not an infection and not contagious, but it should be told apart from cold sores, which are caused by the herpes virus, appear on or around the lips, can also show up inside the mouth as a small group of pinhead-sized ulcers, and are contagious. Most people's ulcers are under 1 cm and heal on their own in 7 to 10 days without a scar; in about one in ten people, ulcers are over 1 cm, can last for weeks and can scar.
They keep coming back because the problem is not some germ in the mouth but the way the lining and the immune system get along: a small irritation, in someone prone to ulcers, is amplified into a local attack.
If an ulcer has not healed after 3 weeks, see a dentist or doctor: most mouth ulcers are harmless, but one that will not heal is occasionally a sign of mouth cancer.
Numbers · How common, and three patterns
Recurrent aphthous stomatitis is the most common lesion of the lining of the mouth, and most people get their first ulcers in childhood or adolescence. How many people have it depends on how and whom you ask: one review puts the prevalence at 5% to 20%, while another reports that when young adults are asked whether they have ever had recurring ulcers, up to 66% say yes. Ulcers become less frequent with age.There are three patterns:
Minor: by far the most common, under 10 mm, usually healed within two weeks, no scar.Major: over 10 mm, an outbreak can last more than six weeks, with a real risk of scarring.Herpetiform: dozens of small, deep ulcers 2 to 3 mm across that often merge, healing within a month without a scar. Despite the name, it is often mistaken for a herpes virus infection, and a doctor may test to rule herpes out.
The bigger, deeper, longer-lasting kind is the one more worth a doctor's look.
Chapter 2
Why the lining is broken from within
An ulcer starts in the surface cells of the mouth lining (keratinocytes). The current understanding is that some still-unidentified trigger makes these cells release inflammatory signals that call in white blood cells. In people prone to ulcers, this response is stronger than usual, and the immune system ends up punching through a small patch of its own lining. In people with these ulcers, an inflammatory signal called is clearly raised in the saliva.
What lights the fire is ordinary: a bite or scrape, a stretch of stress, antigens brought in by bacteria or viruses.
Why do some people never get them while others get them every month? Part of it is genes: people with affected relatives are more likely to have them, and gene variants for inflammatory signals (interleukins and others) are linked to them as well.
This explains something frustrating: topical steroids and other treatments can make an ulcer milder and heal faster, but none of them stops the ulcers coming back. What you can do is give the fire fewer chances to start, and check whether another condition is driving it.
What lights the fire is ordinary: a bite or scrape, a stretch of stress, antigens brought in by bacteria or viruses.
Why do some people never get them while others get them every month? Part of it is genes: people with affected relatives are more likely to have them, and gene variants for inflammatory signals (interleukins and others) are linked to them as well.
This explains something frustrating: topical steroids and other treatments can make an ulcer milder and heal faster, but none of them stops the ulcers coming back. What you can do is give the fire fewer chances to start, and check whether another condition is driving it.
Myth · Can mouth ulcers spread to others
No. Recurrent aphthous ulcers come from your own immune response; there is no germ in them that can pass to anyone else, so sharing cutlery or kissing will not spread them.The thing they get confused with is the cold sore: it is caused by the herpes virus, appears on or around the lips and often starts with tingling, itching or burning; it can also appear inside the mouth as a small group of pinhead-sized ulcers. Cold sores are contagious, so don't assume a sudden cluster of tiny ulcers inside the mouth can't spread.
One more case to tell apart: several ulcers appearing in the mouth at once, together with a rash on the hands and feet, is most likely hand, foot and mouth disease, which is common in children and is contagious.
Chapter 3
What sets ulcers off
A single ulcer is usually set off by something you can watch out for:
Local injury: biting your cheek, badly fitting braces or dentures, a rough filling or sharp tooth, a scrape from hard food, a burn from a hot drink, or brushing too hard.Tiredness, stress or anxiety.A food intolerance or allergy.
Others are harder to control: hormonal changes (such as in pregnancy), family genes, low iron or vitamins, and some medicines.
One counterintuitive trigger is having just quit smoking. Some people get mouth ulcers in the first while after stopping. One explanation is that heavy, long-term smoking exposes the lining to so much nicotine that it grows a protective layer of keratin on its surface, and this layer recedes after quitting. That is not a reason to go back: the protection only exists at very high nicotine levels, at the cost of exposing the whole mouth to tobacco. The ulcers pass; the benefits of quitting stay.
Local injury: biting your cheek, badly fitting braces or dentures, a rough filling or sharp tooth, a scrape from hard food, a burn from a hot drink, or brushing too hard.Tiredness, stress or anxiety.A food intolerance or allergy.
Others are harder to control: hormonal changes (such as in pregnancy), family genes, low iron or vitamins, and some medicines.
One counterintuitive trigger is having just quit smoking. Some people get mouth ulcers in the first while after stopping. One explanation is that heavy, long-term smoking exposes the lining to so much nicotine that it grows a protective layer of keratin on its surface, and this layer recedes after quitting. That is not a reason to go back: the protection only exists at very high nicotine levels, at the cost of exposing the whole mouth to tobacco. The ulcers pass; the benefits of quitting stay.
Evidence · Should you drop SLS toothpaste
Many toothpastes contain sodium lauryl sulfate (SLS), the detergent that makes toothpaste foam. One idea is that it breaks down the protective mucus layer on the lining of the mouth and exposes the cells beneath.The evidence is not fully consistent:
A systematic review pooled 4 double-blind crossover trials (124 people), 2 of them in the combined analysis: with SLS-free toothpaste, people had fewer ulcers, shorter ulcers, fewer episodes and less pain. The authors say better trials are still needed.A randomized trial cited in another review found that SLS-free products helped ulcers heal but did not reduce the number of ulcers or episodes.
How to read it: this is a cheap, harmless experiment. If you get ulcers often, switch to a toothpaste without SLS (an ingredients list that says sodium lauryl sulfate means it has it) and see over a month or two whether you get fewer. The UK National Health Service (NHS) advice for people with mouth ulcers also includes avoiding toothpaste with SLS.
Safety · Medicines that can trigger ulcers
Medicines that the UK National Health Service (NHS) lists as possible triggers of mouth ulcers include some non-steroidal anti-inflammatory drugs (painkillers in the ibuprofen family), beta blockers (a common class of drug for blood pressure and heart rate) and nicorandil (a drug for angina).If your ulcers clearly increase after starting a new medicine, tell the doctor who prescribed it, and don't stop it yourself: each of these drugs treats something, and whether and how to switch is a doctor's decision.
Chapter 4
Recurring ulcers: check the body
An occasional ulcer is usually just about the mouth. But ulcers that keep coming back or are severe are sometimes the body flagging something elsewhere:
Low iron, folate or vitamin B12: these are linked to mouth ulcers, whether one is low or several are. For people who get ulcers repeatedly, a blood count with iron and these two vitamins is a reasonable check (see iron).Coeliac disease: an immune disease of the gut triggered by gluten (a protein in wheat and some other grains). Pooled observational studies show that people with coeliac disease have about 2.5 times the usual risk of mouth ulcers, and mouth signs can appear years before gut symptoms, so recurring ulcers are worth asking a doctor about testing for it even without diarrhea (see Celiac disease).Crohn's disease and other inflammatory bowel diseases: up to about 20% of people with Crohn's disease have mouth lesions.Behçet's disease: besides mouth ulcers, there are genital ulcers, eye inflammation (such as uveitis) and skin lesions.
So if mouth ulcers come with diarrhea, weight loss or anemia, or you also get ulcers elsewhere on the body or red, swollen, painful joints, it is not just about the mouth: see a doctor.
Low iron, folate or vitamin B12: these are linked to mouth ulcers, whether one is low or several are. For people who get ulcers repeatedly, a blood count with iron and these two vitamins is a reasonable check (see iron).Coeliac disease: an immune disease of the gut triggered by gluten (a protein in wheat and some other grains). Pooled observational studies show that people with coeliac disease have about 2.5 times the usual risk of mouth ulcers, and mouth signs can appear years before gut symptoms, so recurring ulcers are worth asking a doctor about testing for it even without diarrhea (see Celiac disease).Crohn's disease and other inflammatory bowel diseases: up to about 20% of people with Crohn's disease have mouth lesions.Behçet's disease: besides mouth ulcers, there are genital ulcers, eye inflammation (such as uveitis) and skin lesions.
So if mouth ulcers come with diarrhea, weight loss or anemia, or you also get ulcers elsewhere on the body or red, swollen, painful joints, it is not just about the mouth: see a doctor.
Evidence · Do vitamin supplements help
Two randomized trials point in opposite directions, and they only make sense read together:The vitamin B12 trial (Volkov 2009): 58 primary care patients with ulcers; one group took a sublingual dose of B12 far above daily needs every day for 6 months, the other a placebo. At months 5 and 6, the B12 group had clearly shorter, fewer and less painful ulcers; in the last month, 74.1% of the B12 group reached "no ulcers at all" versus 32.0% with placebo. The effect appeared whether or not blood B12 was low at the start.The multivitamin trial (Lalla 2012): 160 adults with at least three episodes in a year took a daily multivitamin dosed at the recommended daily intake for up to a year, versus placebo. New episodes (4.19 vs 4.60) and episode length (8.66 vs 8.99 days) did not differ, nor did pain or eating. The authors concluded that clinicians should not routinely recommend multivitamins to prevent ulcers.
How to read them: the first trial is small, uses a large dose and has not been repeated in a big trial; the second is larger, uses everyday doses and was negative. So an everyday-dose multivitamin taken on the off chance probably won't help. For people who really are low in iron, B12 or folate, testing first and supplementing under a doctor's guidance is the targeted approach.
volkov-2009-b12-aphthouslalla-2012-multivitamin-aphthous
Clinical · How many turn out deficient
A case-control study compared 92 adults who get recurring ulcers with 94 who don't. Low iron, , B12 or folate was found in 14.14% of the ulcer group and 6.39% of the controls. The gap looks like double, but it did not reach statistical significance; in other words, most people with recurring ulcers turn out not to be deficient.The authors still recommend a routine blood count with iron, folate and B12 for people with recurring ulcers: one test is cheap, a deficiency can be corrected, and a normal result rules out one cause. In the same study, age and a family history of ulcers were linked to having them.
lopez-jornet-2014-hematinic-aphthous
Chapter 5
Easing an ulcer once it's there
Ulcers need time to heal, and nothing works instantly. What you can do is stop irritating them, so they heal a little faster and hurt a little less:
Use a soft toothbrush, eat softer food, and drink cool drinks through a straw.Avoid very spicy, salty or acidic food, rough crunchy food such as crisps or toast, and very hot or acidic drinks (such as fruit juice).Don't use toothpaste containing SLS.You can rinse with salt water: half a teaspoon of salt dissolved in a glass of warm water; rinse and spit it out, don't swallow.
Pharmacies sell, without a prescription, antimicrobial mouthwash, painkilling gels or sprays, and steroid lozenges. On the evidence, topical steroids may reduce new ulcers, ease pain and speed healing a little (low-quality evidence); chlorhexidine mouthwash may reduce how severe and painful ulcers are (very low-quality evidence). If the pain stops you eating, or the ulcers are large and many, a doctor can prescribe something stronger.
All of this only makes one episode easier; none of it prevents the next.
Use a soft toothbrush, eat softer food, and drink cool drinks through a straw.Avoid very spicy, salty or acidic food, rough crunchy food such as crisps or toast, and very hot or acidic drinks (such as fruit juice).Don't use toothpaste containing SLS.You can rinse with salt water: half a teaspoon of salt dissolved in a glass of warm water; rinse and spit it out, don't swallow.
Pharmacies sell, without a prescription, antimicrobial mouthwash, painkilling gels or sprays, and steroid lozenges. On the evidence, topical steroids may reduce new ulcers, ease pain and speed healing a little (low-quality evidence); chlorhexidine mouthwash may reduce how severe and painful ulcers are (very low-quality evidence). If the pain stops you eating, or the ulcers are large and many, a doctor can prescribe something stronger.
All of this only makes one episode easier; none of it prevents the next.
Evidence · How well the topical treatments work
A systematic review in BMJ Clinical Evidence graded the topical treatments one by one using GRADE:Topical steroids: may reduce new ulcers, ease pain and speed healing without notable side effects; low-quality evidence. Read the size of the effect carefully: in one trial of 240 people, ulcers treated with dexamethasone ointment healed in 6 days on average versus 7 with placebo, about a day faster.Antiseptic mouthwashes such as chlorhexidine: may reduce how severe and painful ulcers are, but studies disagree on whether they reduce new ulcers; very low-quality evidence.Local painkillers and tetracycline mouthwash: the evidence is too weak to say whether they work.
Another review sums it up: topical steroids and most other treatments only make ulcers milder; they do not stop them recurring. So for people who get ulcers often, cutting down triggers and finding any underlying cause matters more than a drawer full of remedies. Whether to use a steroid, and which one, is for a doctor or pharmacist to decide.
Chapter 6
When to see a doctor
Most mouth ulcers heal on their own within a week or two. But see a dentist or doctor in these situations:
An ulcer has not healed after 3 weeks. An ulcer that won't heal is occasionally a sign of mouth cancer and needs a face-to-face examination.It is different from the ulcers you usually get: especially large, or near the back of the throat.The ulcer bleeds, or becomes more painful and redder, which may mean it has become infected.You also get ulcers elsewhere on your body (skin, genitals), or red, swollen, painful joints.The ulcers come with diarrhea, weight loss or anemia.A child has fevers that come back on a cycle, each time with mouth ulcers and a sore throat: tell the pediatrician, as this can be a periodic fever syndrome.
This list is not a diagnosis. It only tells you when to stop handling things yourself and have a doctor look in person.
An ulcer has not healed after 3 weeks. An ulcer that won't heal is occasionally a sign of mouth cancer and needs a face-to-face examination.It is different from the ulcers you usually get: especially large, or near the back of the throat.The ulcer bleeds, or becomes more painful and redder, which may mean it has become infected.You also get ulcers elsewhere on your body (skin, genitals), or red, swollen, painful joints.The ulcers come with diarrhea, weight loss or anemia.A child has fevers that come back on a cycle, each time with mouth ulcers and a sore throat: tell the pediatrician, as this can be a periodic fever syndrome.
This list is not a diagnosis. It only tells you when to stop handling things yourself and have a doctor look in person.
Red flag · Mouth, genitals and eyes together
Behçet's disease is a form of vasculitis, and one of its signs is mouth ulcers that look just like aphthous ulcers; in about 80% of people with Behçet's, mouth ulcers are the first sign. So the mouth ulcers alone often can't tell you which it is.What sets it apart from ordinary mouth ulcers is what happens outside the mouth:
Genital ulcers.Eye inflammation: anterior or posterior uveitis, which may show as a red, painful eye, sensitivity to light or blurred vision.Skin lesions, such as painful red lumps on the legs.
If your mouth ulcers keep coming back and genital ulcers or skin lesions appear as well, see a doctor soon. A red, painful eye, sensitivity to light or blurred vision needs a doctor the same day; if you cannot see, go to the emergency department now.
nhs-uveitis
References · 7
- Staines, K., & Greenwood, M. (2015). Aphthous ulcers (recurrent). BMJ Clinical Evidence, 2015, 1303. Most people develop a few ulcers under 10 mm that heal in 7-10 days without scarring; in 10% lesions exceed 10 mm and can scar; up to 66% of young adults give a history consistent with recurrent aphthous ulceration, lessening with age; most are idiopathic, local physical trauma may trigger ulcers in susceptible people. Topical corticosteroids may reduce new ulcers, pain and healing time without notable adverse effects (low-quality evidence; e.g. one RCT of 240 people, mean ulcer duration 6 days with dexamethasone ointment vs 7 with placebo); chlorhexidine rinses may reduce severity and pain, inconclusive for new ulcers (very low); local analgesics and tetracycline mouthwash: unknown (full text PMC4356175; PMID 25720501). pmc.ncbi.nlm.nih.gov/articles/PMC4356175
- NHS. (2024). Mouth ulcers. Usually clear up within a week or 2; see a GP or dentist if one lasts longer than 3 weeks, is different from previous ulcers (bigger, near the back of the throat), or bleeds or becomes more painful and red; a long-lasting mouth ulcer is sometimes a sign of mouth cancer. Also see a GP with ulcers elsewhere (skin, genitals) or painful, red or swollen joints. Not contagious; not to be confused with cold sores. Causes: biting the cheek, badly fitting dentures or braces, rough fillings or a sharp tooth, cuts or burns from hard food or hot drinks, food intolerance or allergy, toothbrush damage or irritating toothpaste, tiredness, stress or anxiety; hormonal changes, genes, deficiency of iron, zinc, folic acid, vitamin B or D, medicines including some NSAIDs, beta blockers or nicorandil, and stopping smoking. Several ulcers may be hand, foot and mouth disease, oral lichen planus, Crohn's or coeliac disease, or a weakened immune system (HIV, lupus). Self-care: soft toothbrush, cool drinks through a straw, softer foods; avoid very spicy, salty or acidic food, rough crunchy food, very hot or acidic drinks such as fruit juice, and toothpaste containing sodium lauryl sulphate. Pharmacy: antimicrobial mouthwash, painkilling gel or spray, corticosteroid lozenges, salt mouthwash (half a teaspoon of salt in a glass of warm water, rinse and spit). A GP or dentist may prescribe stronger medicine for severe, persistent or infected ulcers. www.nhs.uk/conditions/mouth-ulcers
- Scully, C., & Porter, S. (2008). Oral mucosal disease: recurrent aphthous stomatitis. British Journal of Oral and Maxillofacial Surgery, 46(3), 198-206. Recurrent, small, round or ovoid ulcers with erythematous haloes and yellow or grey floors, usually first in childhood or adolescence; genetic predisposition with interleukin genotype associations and sometimes a family history; diagnosis is clinical and must be differentiated from Behcet disease (aphthous-like ulcers with genital ulceration and eye disease, particularly posterior uveitis). Topical corticosteroids and most other treatments reduce severity but do not stop recurrence (abstract, PMID 17850936). 10.1016/j.bjoms.2007.07.201
- Edgar, N. R., Saleh, D., & Miller, R. A. (2017). Recurrent aphthous stomatitis: a review. Journal of Clinical and Aesthetic Dermatology, 10(3), 26-36. Minor aphthae under 10 mm typically resolve within 14 days; major aphthae over 10 mm may persist over six weeks and pose a scarring risk; herpetiform RAS: dozens of small deep ulcers that coalesce, non-scarring, resolve within one month, commonly misdiagnosed as herpetic gingivostomatitis, so testing to rule out herpes simplex is reasonable; minor over 70% of cases, major 10%, herpetiform 10%. An unknown antigen is thought to stimulate keratinocytes, causing cytokine secretion and leukocyte chemotaxis; TNF-alpha is significantly increased in the saliva of RAS patients. SLS was postulated to denature the oral mucin layer; a randomised trial found SLS-free products helped ulcer healing but did not reduce the number of aphthae or episodes. Several studies report a protective effect of smoking; a cross-sectional survey concluded it is protective only at very high nicotine levels that form a protective keratin layer over the mucosa. Deficiencies of vitamin B12, folate and iron have been associated with aphthous stomatitis; IBD, coeliac disease and malabsorption commonly associated; oral lesions of coeliac disease may precede gastrointestinal symptoms by several years, so screening should be done even without gastrointestinal lesions; oral lesions in up to 20% of Crohn's disease. Behcet's disease: a vasculitis with oral and genital ulceration, aphthosis the presenting sign in 80%, anterior or posterior uveitis, skin lesions such as erythema nodosum. Recurrent fever with ulcers prompts workup for autoinflammatory syndromes such as PFAPA and cyclic neutropenia. First-line treatment is topical, systemic only as necessary (full text PMC5367879; PMID 28360966). pmc.ncbi.nlm.nih.gov/articles/PMC5367879
- Slebioda, Z., Szponar, E., & Kowalska, A. (2013). Recurrent aphthous stomatitis: genetic aspects of etiology. Postepy Dermatologii i Alergologii, 30(2), 96-102. Prevalence 5-20% depending on method and group; an enhanced immunologic response to triggers such as mechanical injury, stress or bacterial and viral antigens; higher prevalence in relatives and polymorphisms in proinflammatory cytokine genes suggest a genetic background (abstract, PMID 24278055). 10.5114/pdia.2013.34158
- Zhao, Y., & Feng, W. (2026). Relative risk of oral manifestations with celiac disease: a systematic review and meta-analysis. BMC Gastroenterology, 26. 22 observational studies; pooled prevalence of oral manifestations in coeliac disease 21.41%; recurrent aphthous stomatitis RR 2.45 (95% CI 1.67-3.60), dental enamel defects RR 2.49, xerostomia RR 5.99; oral signs support screening for coeliac disease in at-risk people (abstract, PMID 42021157). 10.1186/s12876-026-04860-z
- Alli, B. Y., Erinoso, O. A., & Olawuyi, A. B. (2019). Effect of sodium lauryl sulfate on recurrent aphthous stomatitis: a systematic review. Journal of Oral Pathology & Medicine, 48(5), 358-364. Four double-blind crossover RCTs (124 participants), two in the main meta-analysis: SLS-free dentifrice reduced the number of ulcers, ulcer duration, number of episodes and ulcer pain compared with SLS-containing; better trials still required (abstract, PMID 30839136). 10.1111/jop.12845