A mouth ulcer that appeared after you bit your cheek at dinner and one that keeps coming back every month are usually the same kind of sore, but they call for different responses. The first needs little more than patience and something soothing. The second is worth investigating, because recurring ulcers often have a trigger that can be found and removed.
Most ulcers clear by themselves within about 10 to 14 days. What matters more than how much an ulcer hurts is how long it lasts and how it looks and feels. Any sore in the mouth that has not healed or has changed within 3 weeks should be checked by a dentist or GP.
Small, painful and usually harmless
The common mouth ulcer is called an aphthous ulcer, or canker sore in North America. It is a shallow break in the soft lining of the mouth, usually round or oval, with a pale yellow or grey base and a red rim. You will typically find one on the inside of the lips or cheeks, under or along the sides of the tongue, or on the floor of the mouth. They rarely form on the firm gum attached to the teeth or on the hard palate.
Recurring aphthous ulcers are common. The Victorian Government's Better Health Channel puts the figure at around 20 per cent of the population. The sting can feel far bigger than the sore itself, particularly with salty, sour or spicy food, because the sore exposes sensitive tissue right at the surface. That level of discomfort is normal for an ulcer and is not, on its own, a warning sign.
Size and number tell you which type you have
DermNet, the New Zealand dermatology reference, describes three patterns.
Minor ulcers
About 80 per cent of aphthous ulcers are this type. They are less than 5 mm across, may come one or a few at a time, and heal within one to two weeks without leaving a mark.
Major ulcers
These are larger, often more than 10 mm, deeper and more painful. They can take weeks or months to heal and may leave a scar. A major ulcer deserves a professional assessment, both to confirm what it is and because stronger treatment is often needed.
Herpetiform ulcers
Despite the name, these are not caused by the herpes virus. They appear as many pinpoint sores, often on the tongue, that can join together into a larger ragged area. They usually settle within about a month.
Recurring ulcers usually have a trigger
Nobody fully understands why some people get the odd ulcer while others get them constantly. DermNet notes that about 40 per cent of people with aphthous ulcers have a family history of them. The useful part for patients is that an ulcer is often set off by something, and finding that something is the most practical way to have fewer of them.
Injury inside the mouth. Biting your cheek, a scratch from a hard crust, an over-enthusiastic toothbrush or a denture that rubs can all start an ulcer. So can the jagged edge of a cracked tooth or a broken filling. When ulcers keep appearing in exactly the same spot, a sharp edge nearby is the first thing a dentist will look for.
Stress, illness and tiredness. Many people notice ulcers during exams, busy periods at work or after a run of poor sleep. Better Health lists stress, illness and extreme tiredness as factors that can make ulcers worse.
Low iron, folate or B vitamins. Deficiencies of iron, folate and B vitamins are linked to recurring ulcers. People with heavy periods, plant-based diets that are not well planned, or conditions that affect absorption, such as coeliac disease, are more likely to run low without knowing it. A blood test through your GP can check.
Hormonal changes. Some women find their ulcers line up with their menstrual cycle.
Certain foods. Chocolate is one commonly reported trigger, and a food intolerance or allergy can be behind some ulcers, although food triggers affect only some people. A simple food diary over a few months can show a pattern.
Toothpaste foaming agents. Sodium lauryl sulfate (SLS) is the detergent that makes many toothpastes foam. A 2019 systematic review by Alli and colleagues in the Journal of Oral Pathology and Medicine pooled small crossover trials and found that people with recurring ulcers had fewer, shorter and less painful ulcers when using SLS-free toothpaste. The authors called for better trials, so treat it as a sensible experiment rather than a cure.
Medicines and medical conditions. Some medicines can cause mouth ulcers, including nicorandil, a heart medicine, some anti-inflammatory painkillers and some cancer treatments. Never stop a prescribed medicine yourself; raise it with your doctor. Recurring ulcers can also be linked to coeliac disease, inflammatory bowel disease and, rarely, conditions such as Behçet's disease. If your pattern of ulcers changes suddenly, or ulcers come with gut symptoms, sore eyes or genital sores, see your GP.
Easing the pain while it heals
Better Health is frank that the healing of an ulcer cannot really be hurried, but the soreness can be managed. Most people need nothing more than the first few of these steps.
- Salt water rinses. Dissolve about half a teaspoon of salt in a glass of warm water and rinse gently a few times a day.
- Change what you eat for a few days. Soft, bland food at a comfortable temperature hurts less. Avoid spicy, salty and sour foods and drink cool water through a straw if needed.
- Pharmacy gels and paints. Numbing gels containing a local anaesthetic, protective barrier pastes and anti-inflammatory rinses can make eating easier. A pharmacist can suggest one that suits you. Check with them before using an adult ulcer gel on a child, as not every product is suitable for children.
- An alcohol-free antiseptic mouthwash. Chlorhexidine mouthwash can help keep the area clean when brushing is uncomfortable. Use it for short periods only, as it can stain teeth.
- Brush gently around the sore. Keep cleaning the rest of your mouth. Plaque left sitting near an ulcer only adds to the irritation, and a sore mouth that is not being cleaned can lead to bad breath as well.
For large, very painful or frequent ulcers, a dentist may recommend a topical corticosteroid, a steroid paste or mouthwash applied to the ulcer, to reduce pain and inflammation. These need professional advice on how and how long to use them.
Signs that an ulcer needs to be seen
Most ulcers can be managed at home. Book with a dentist or GP if any of the following apply.
- A sore that has not healed or has changed within 3 weeks, however small it is.
- An ulcer that does not hurt. Ordinary ulcers are painful, so a painless sore you only notice by chance is more of a concern.
- A firm, raised or rolled edge, or a sore that feels hard when you press near it.
- Bleeding without any obvious cause, or a red or white patch that will not go away.
- Numbness of the lip, tongue or chin, or a lump in the neck.
- Ulcers that come very often, are very large, or leave you unable to eat or drink properly.
- Ulcers that began after starting a new medicine.
Smoking and regular drinking both raise the risk of mouth cancer, which is one more reason not to ignore a sore that is slow to heal. Most slow ulcers turn out to be harmless, but a quick look is the only way to be sure. Our guide to oral cancer screening explains what that check involves.
Sores that are not aphthous ulcers
Cold sores are caused by the herpes simplex virus. They usually show up on or around the outside of the lips as a tingling patch, then a cluster of small blisters that break and crust. They are contagious, while aphthous ulcers are not. Antiviral creams from a pharmacy work best when started at the first tingle. The differences are set out in more detail in our cold sores and mouth ulcers comparison.
Oral thrush is a yeast infection that forms creamy white patches which can often be wiped off, leaving red, sore tissue. It is more likely after antibiotics, with dentures, with dry mouth, or in people using steroid inhalers who do not rinse afterwards. It needs antifungal treatment.
A dental abscess can look like a sore or pimple on the gum near one tooth, often with swelling, throbbing or a bad taste. It will not heal like an ulcer and usually needs treatment of the tooth itself. See our guide to the signs of a tooth abscess.
Having fewer ulcers
If you can find your trigger, prevention tends to work well. If no trigger turns up, the steps below still help some people.
Ask your dentist to smooth any sharp tooth, filling or denture edge you can feel with your tongue. Try an SLS-free toothpaste for at least a couple of months and keep a note of how many ulcers you get. If ulcers are frequent, ask your GP about a blood test for iron, folate, vitamin B12 and coeliac disease. Eat hard, crunchy foods more slowly. If a tooth near a recurring sore is also sensitive to cold or sweet, mention it, as a crack or worn filling may be part of the story.
Regular check-ups and cleans help too. Your dentist or OHT can spot rough edges early and keep plaque and tartar under control. Our guide to dental cleans covers what a clean involves.
When you come to Lumi with an ulcer
A mouth ulcer can be looked at during a routine examination, or you can book a visit just for it. The dentist will examine the ulcer and the tissue around it, check nearby teeth, fillings and any denture for rough edges, and feel the floor of the mouth and the neck. Depending on what is found, the next step may be advice on home care, a steroid paste or mouthwash, a blood test through your GP, or referral to an oral medicine specialist for a closer look or biopsy. Healing times vary between people, so we will not promise how quickly an ulcer will settle.
Questions about mouth ulcers
Are mouth ulcers contagious?
No. Aphthous ulcers cannot be passed on through kissing or sharing a cup. Cold sores, which are often confused with them, are contagious.
Why does an ulcer keep coming back in the same place?
Repeated injury is the most likely reason. A sharp tooth, a broken filling or a denture that rubs can keep damaging the same patch of lining. Fixing the edge usually matters more than treating the ulcer.
Is an ulcer on the tongue more worrying?
Ulcers on the tongue are common and most heal normally. How long a sore lasts, and whether it is hard, raised or painless, matters more than where it is. The sides and underside of the tongue are among the sites where mouth cancer is more often found, so do not wait beyond 3 weeks for a tongue sore that has not healed.
Do frequent ulcers mean I am low in a vitamin?
Not always, but low iron, folate and B vitamins are a known cause and easy to check with a blood test. If your results are normal, stress, injury, hormones or toothpaste may be the more likely trigger.
If an ulcer is worrying you or keeps returning, you can contact Lumi Dental in Melrose Park to arrange an assessment, or see our current new patient offers.
