What causes mouth ulcers, and what can be done about them?

Most mouth ulcers are caused by trauma — a sharp tooth, a bitten cheek, a burn — or are recurrent aphthous ulcers, the common “canker sores” that affect around a fifth of the population. Once an ulcer has formed it is very hard to treat directly; treatment is mostly about relieving symptoms while it heals and removing whatever caused it so it does not come back.

The more important part of this article is the last section. Most ulcers are harmless and resolve in one to two weeks. A small number are not, and the distinguishing features are worth knowing.

Before anything else: when this is a hospital problem

An ulcer by itself is not an emergency. These are. Go to a hospital emergency department, or call 000, if any of the following are present:

• Facial swelling that is spreading, especially toward the eye or down into the neck or under the jaw
• Difficulty breathing or swallowing, or a change in your voice
• Fever alongside mouth or dental pain
• Bleeding from the mouth that will not stop

These suggest a spreading infection or a bleed that needs same-day hospital care, not an appointment. Where an infection has started in a tooth rather than the soft tissue, what is a tooth abscess? and can a dental abscess affect your general health? explain why that is treated urgently.

For a sharp broken tooth cutting the cheek, or an ulcer with severe pain that cannot wait, emergency dentistry covers what can be seen on the day.

What a mouth ulcer is

A mouth ulcer is a breakdown of the delicate tissue lining the mouth. It presents as swelling, tenderness, and irritation from spicy or salty food, and usually causes moderate to extreme discomfort when eating and speaking. The pain is out of proportion to the size, because the tissue is thin, well supplied with nerves, and constantly moving.

Common causes

• Trauma — rubbing against a sharp tooth or a rough denture, biting the cheek or tongue, or burns from hot food such as melted cheese or hot soup. Why do I bite my cheek after a filling? covers the version of this that follows dental work, and my denture is broken — what should I do? the version caused by a damaged appliance
• Psychological stress
• Nutritional deficiencies — particularly vitamin B12, zinc, folic acid and iron
• Gastrointestinal tract disease — for example coeliac disease and Crohn's disease
• Impaired immunity
• Recurrent aphthous stomatitis (RAS), or canker sores — characterised by regular recurring ulcers, affecting about one-fifth of the population. The cause is not completely understood.

Some additions worth knowing, because they are commonly missed:

• Sodium lauryl sulfate (SLS) in many toothpastes is associated with more frequent aphthous ulcers in susceptible people. Switching to an SLS-free toothpaste is a cheap, low-risk experiment for anyone with frequent recurrences — choosing the right toothpaste and with so many toothpastes on the market, how can I make a wise choice? cover how to read the ingredients panel.
• Medications — some drugs cause oral ulceration as a side effect, and many also cause dry mouth, which makes ulcers both more likely and slower to heal. Bring your medication list to the appointment.
• Diabetes, particularly where blood glucose is not well controlled. Diabetes Australia lists among its oral complications both "delayed or poor healing of wounds in the mouth, such as mouth ulcers" and "dry mouth, which can lead to ulcers and infections" — so diabetes can both cause ulcers and slow their healing. Diabetes and oral health.
• Hormonal changes are a recognised trigger in some people — see are women especially prone to oral health problems? and, in pregnancy, pregnancy and dental health.
• Orthodontic appliances cause repeated trauma ulcers, usually settled with orthodontic wax over the offending bracket or wire — see braces, and Invisalign where the irritation is from an aligner edge.
• New or ill-fitting dentures rub until they are adjusted. Five things you should know about your new dentures and caring for yourself and your immediate dentures cover the settling-in period, and dentures the appliance itself.
• Viral causes — primary herpes simplex in children, and hand, foot and mouth disease, produce multiple ulcers alongside fever and general illness. These are a different problem from a single aphthous ulcer.
• Vaping and smoking irritate the lining and slow healing. The Australian Dental Association notes that smoking "can cause sores in your mouth to heal slowly", because of decreased blood flow to the gums — the effects of vaping on your oral health.

What helps

Once an ulcer forms it is very hard to treat, and nothing reliably makes it disappear overnight. The following can alleviate symptoms while it heals:

• Deal with the cause of trauma. Have your dentist smooth any sharp tooth, rough filling edge or ill-fitting denture. This is the only intervention in the list that stops the ulcer recurring rather than just easing it, and it is the one most often skipped. A sharp edge from a broken tooth or a lost filling is worth booking for — see chipped and cracked teeth and what do I do if a temporary filling comes out?
• Salt or sodium bicarbonate mouth rinse. Dissolve a teaspoon of salt or bicarbonate of soda in a glass of water and rinse. Cheap, safe, and genuinely useful.
• Topical pharmacy preparations. Anti-inflammatory and anaesthetic gels and rinses are available over the counter and can be used as directed on the packaging. They numb and soothe rather than heal.
• L-Lysine tablets are sometimes suggested to promote healing. The evidence for lysine in aphthous ulcers is limited and not strong; some people find it helpful. Take as directed, and speak to your pharmacist or doctor if you take other medications.

Avoid alcohol-containing mouthwashes while an ulcer is present. This is not a preference — Australian Prescriber states that essential-oil mouthwashes, which are the high-alcohol category, "are not recommended for patients suffering from xerostomia, dental erosion due to a low oral pH, or oral mucosal disease", because of ethanol-induced mucosal irritation and dryness. A review in the Australian Dental Journal is more specific about what high alcohol concentrations in rinses can do to the lining: "epithelial detachment, keratosis, mucosal ulceration, gingivitis, petechiae and oral pain." The truth and myths about mouthwashes and should I be using mouthwash as well as brushing and flossing? cover the general case.

Practical measures that make the healing period more bearable:

• Avoid spicy, salty, acidic and very hot food while it heals — how does acidic food affect your teeth? is relevant for a different reason, but the same list of foods applies
• Use a soft toothbrush and keep brushing — keeping the mouth clean shortens healing. Which toothbrushes do dentists recommend?, and see over brushing, because pressing harder around a sore area makes it worse
• Avoid SLS toothpaste during an outbreak
• Over-the-counter pain relief taken according to the packet

Do not place aspirin against the ulcer or gum. It causes a chemical burn of the soft tissue and makes the problem worse, not better. The same applies to clove oil applied neat, and to any tablet held in the cheek.

If ulcers recur frequently, ask your doctor about a blood test for iron, B12, folate and zinc, and about screening for coeliac disease. A deficiency found and corrected is one of the few things that stops recurrent ulcers properly. The mouth is often where a general health problem shows first — health problems linked to poor oral hygiene and the importance of dental hygiene: a window onto your overall health develop that point.

When to get it looked at

This is the part that matters most. See your dentist or doctor to investigate any mouth ulcer that:

• Is very large
• Takes longer than two to three weeks to heal
• Causes extreme, intolerable pain
• Is associated with high fever and a general feeling of ill health
• Frequently recurs

The two-to-three-week rule is the important one, and it is not a house rule. The Better Health Channel, published by the Victorian Department of Health, puts it as plainly as possible: "if you notice a mouth ulcer that lasts for longer than 2 weeks, get it checked by a dentist as soon as you can."

The reason is set out in the Australian Journal of General Practice, the RACGP's peer-reviewed journal: "initial lesions of oral cancer are generally painless, and hence, patients reporting any unexplained and/or non-healing changes or symptoms in the mouth for more than two to three weeks (eg a persistent ulcer, red patches, lumps, a sore throat, or erythematous or speckled lesions) should have an oral cancer screen."

Read the word painless there carefully. An ulcer that is not sore but does not heal is more concerning than one that hurts a great deal and resolves in a week. That is the opposite of how most people triage their own symptoms, and it is why delay is common: the same paper records that an Australian study found an average diagnostic delay of approximately four months between symptom onset and initial histological diagnosis.

Other features that warrant prompt assessment — the RACGP's own list of common signs is "unexplained mouth ulcer or lump; unexplained neck lump; white or red patches (eg leucoplakia) of oral mucosa; unexplained tooth mobility or non-healing extraction site":

• A lump, or a raised or hardened edge to the ulcer
• A red or white patch that persists
• An ulcer on the side or underside of the tongue, or on the floor of the mouth — the paper identifies "the lateral margins of the tongue and the floor of the mouth" as the highest-risk sites
• Numbness, difficulty swallowing, or a persistent sore throat
• Unexplained bleeding, or a lump in the neck

Who should be looked at more attentively, in the same source: risk-associated screening "should be done on a case-by-case basis for patients aged 45 years or over and for those who are current or past substance users (eg alcohol, tobacco or betel nut/quid)." The Better Health Channel makes the same point for dental check-ups — they are "especially important for those who smoke or regularly drink alcohol, and even more so for those who do both."

Oral cancer: how your dentist can help with early detection and oral cancer: signs, risk factors and how your dentist can help set out the risk factors and what the examination involves; what are the causes, symptoms and treatment of mouth cancer? covers what happens after a referral. Where a biopsy or further surgical assessment is needed, that is the work of an oral and maxillofacial surgeon — what does oral and maxillofacial surgery involve? describes the scope.

Routine dental examinations include a soft-tissue check for precisely this reason, and in practice it is frequently the only screening for oral cancer that anyone receives — the RACGP paper notes that "there is limited evidence to implement a formalised population oral cancer screening program, such as that for cervical cancer screening," so detection "is reliant on recording a thorough medical history and visual examination." It also notes that this screening can be done by GPs as well as dental practitioners, so either is a reasonable place to start. How often should I go to the dentist? and dental cleans with our hygienists cover the interval; if the appointment itself is the obstacle, dental anxiety and how can I ease my anxiety about visiting the dentist? are worth reading first.

Common questions

Which mouthwash should I use while I have an ulcer — or should I use one at all?

The counterintuitive answer is that the strongest antiseptic rinse is usually the wrong choice.

Australian Prescriber's review of mouthwashes as a product class — the most senior Australian clinical source on this, though it dates from 2009 and predates later Cochrane reviews — sorts them by what they are for:

• Sodium bicarbonate is described as “bland and will not irritate the oral mucosa in patients with xerostomia or oral ulcerative disease”, which is the technical endorsement of the teaspoon-in-a-glass-of-water advice above. It also raises salivary pH.
• Chlorhexidine is “currently the most effective mouthwash for reducing plaque and gingivitis”, but the same article warns that it “may also potentiate oral discomfort in patients with chemotherapy-induced mucositis, xerostomia or ulcerative oral mucosal conditions.” In other words, the rinse most people reach for as the serious option can make an ulcer feel worse. It is also recommended “only as a short-term treatment”, with staining, taste alteration, burning and mucosal irritation among its listed adverse effects.
• Benzydamine hydrochloride, an analgesic and anti-inflammatory agent added to some rinses, is the one specifically indicated here: the article recommends it “for radiation-induced oral mucositis and ulcerative mucosal conditions such as recurrent aphthous ulcerative disease.”
• High-alcohol rinses are the category to leave alone while the lining is broken, for the reasons set out above.

The framing that applies to all of them is the article's own: “mouthwashes are an adjunct to, not a substitute for, regular brushing and flossing”, and they “should only be used for short periods of time and should never be the sole means of oral hygiene.” Ask your pharmacist which active ingredient is in the product you are holding, rather than choosing by the word on the front of the bottle.

I have read that alcohol mouthwash causes oral cancer. Is that settled?

No, and this page is not going to pretend otherwise, because the two most relevant sources genuinely disagree and the disagreement is the useful part.

The Australian position comes from a 2008 narrative review in the Australian Dental Journal by McCullough and Farah, which concluded that “there is now sufficient evidence to accept the proposition that alcohol-containing mouthwashes contribute to the increased risk of development of oral cancer”, and that “it is inadvisable for oral healthcare professionals to recommend the long-term use of alcohol-containing mouthwashes.” That paper is where most of the figures circulating on Australian dental websites originate. It is a narrative review, with no stated search strategy and no pooled estimate.

The largest international estimate is a 2016 pooled analysis in the European Journal of Cancer Prevention from the International Head and Neck Cancer Epidemiology Consortium, covering 8,981 cases of head and neck cancer and 10,090 controls across 12 case-control studies, adjusted for study, age, sex, pack-years of smoking, alcoholic drinks per day and education. Its headline result is null: compared with never users, the odds ratio for all head and neck cancers was 1.01 (95% CI 0.94–1.08) for ever users. Two subgroup signals were statistically significant and are why the question has not simply gone away — oropharyngeal cancer, OR 1.28 (95% CI 1.06–1.56), and use more than once per day, OR 1.31 (95% CI 1.09–1.58). The authors state their own limitations plainly: the analysis is “limited by the retrospective nature of the study and the limited ability to assess risks of mouthwash use in nonusers of tobacco and alcohol.”

What can honestly be said: overall mouthwash use is not associated with head and neck cancer in the largest analysis available; heavy, daily, decades-long use shows a small association that these data cannot establish as causal; and the pooled analysis measured mouthwash use, not ethanol concentration, so it cannot settle the specific question about alcohol-containing products either way.

What that means for you is unglamorous. Mouthwash is an adjunct and is not meant to be a daily lifelong habit in the first place; the separate and much larger risks for oral cancer are tobacco and alcohol consumed together — the Australian review cites a case-control estimate of roughly 50-fold greater risk (OR 50.65; 95% CI 19–134) in heavy smokers and drinkers than in people who never smoked and never drank. If you want to reduce your oral cancer risk, that is where the arithmetic is, not in the rinse cupboard.

The same spot keeps ulcerating. Is that different from getting them in different places?

Yes, and the distinction is the most useful thing on this page for anyone with recurrent ulcers.

Ulcers that appear in different places each time point toward the systemic and aphthous group — the deficiencies, the gastrointestinal conditions, the medication effects, the SLS sensitivity, the hormonal pattern. That is the situation where the blood tests are worth asking for, and where changing toothpaste is worth trying.

An ulcer that keeps returning to the same spot is a different problem, and it usually means something is repeatedly injuring that spot: a sharp cusp, a fractured filling edge, a denture flange, an orthodontic bracket, or a habit of catching the cheek between the teeth. The ulcer is the symptom; the edge is the cause, and no rinse or gel will fix it. Have the site looked at with the specific question “what is rubbing here?”

There is a third possibility that is the reason not to simply keep managing it at home. Chronic repeated trauma to one site, and any lesion that will not heal at one site, are exactly the presentations the RACGP guidance is written about — “unexplained and/or non-healing changes or symptoms in the mouth for more than two to three weeks”. A recurring ulcer that never quite clears at the same location is not the same as a fresh ulcer at the same location, and only an examination can tell those apart.

What will actually happen if I bring one in?

Less than people expect, which is part of why it is worth doing.

The assessment is a history and a look. The RACGP is explicit that in the absence of a population screening programme, detection “is reliant on recording a thorough medical history and visual examination” — so expect questions about how long it has been there, whether it has changed, your general health, your medications, and your smoking and alcohol history, followed by a systematic look at the tongue including its lateral margins and underside, the floor of the mouth, the cheeks, the palate and the throat, and a feel along the neck for lymph nodes. Bringing a written list of your medications makes the history part much more useful.

Three outcomes are common. Most often the cause is identified and dealt with on the spot — a sharp edge smoothed, a denture adjusted, advice on the rinse and on what to avoid while it heals. Sometimes the answer is a review appointment in two weeks to see whether it has gone, which is a reasonable and deliberate plan rather than a brush-off. Less often, a lesion that does not fit is referred for biopsy, which is the definitive test; that is the work of an oral and maxillofacial surgeon, and what does oral and maxillofacial surgery involve? describes the scope.

The point worth holding onto is the Australian study cited above, in which the average delay between symptom onset and histological diagnosis was around four months. Almost none of that delay is in the clinic. It is in the weeks people spend deciding whether an ulcer is worth an appointment.

Related reading

• My mouth is always dry — why is this and does it affect my teeth?
• How do I get rid of my bad breath? — ulcers and dry mouth both contribute
• What to do if you suffer from sensitive teeth
• What is gum disease?
• Five questions you've always wanted to ask your dentist
• Dental myths exposed
• What is the ideal daily routine for oral hygiene?

Practical details

Specialist registration can be verified on the AHPRA register, or by calling 1300 419 495. The practice's registered specialists are identified as such within the full team.

Smile Solutions, Level 1, 220 Collins Street, Manchester Unity Building, Melbourne VIC 3000 — getting here. Phone 13 13 96, contact us, or theteam@smilesolutions.com.au. Monday–Friday 8.00am–6.00pm, Saturday 8.30am–1.30pm, Sunday by appointment. Published fees are in the price guide.

Published 11 August 2013, by Dr Madeleine Hoopmann. General information only; it does not replace advice from your treating practitioner. Medicines named here are examples of over-the-counter products; use any medication only as directed and check with your pharmacist or doctor. Mouthwash product-class statements are from Australian Prescriber (2009); the head and neck cancer figures are from the INHANCE pooled analysis (2016) and the Australian Dental Journal review (2008), which reach different conclusions and are both cited above for that reason.

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