Why Do Mouth Ulcers Keep Coming Back? Causes and Prevention

A mouth ulcer can make a simple cup of tea, a spicy supper or brushing your teeth surprisingly uncomfortable. If you are asking what causes recurring mouth ulcers, the answer is often a combination of everyday triggers and individual sensitivity. Most ulcers are harmless and clear within one to two weeks, but frequent or persistent ulcers are worth taking seriously.

Mouth ulcers are small, painful sores that usually develop inside the mouth, on the tongue, gums, cheeks or lips. They are not the same as cold sores, which tend to occur on or around the outside of the lips and are contagious. Recurring mouth ulcers, sometimes called recurrent aphthous ulcers, can appear every few weeks or months and may have more than one cause.

What causes recurring mouth ulcers?

For many people, there is no single explanation. A minor injury may start one ulcer, while stress, a food trigger or low iron stores make another more likely. Looking for a pattern can help you narrow down what is affecting you.

Small injuries inside the mouth

A sharp tooth edge, poorly fitting dentures, braces, a hard toothbrush or accidentally biting your cheek can damage the lining of the mouth. Even vigorous brushing can be enough to trigger an ulcer in someone prone to them.

Check whether ulcers tend to appear in the same spot. If they do, arrange a dental check-up, particularly if you have a rough filling, broken tooth or denture that rubs. Removing the source of irritation can make a real difference.

Stress, tiredness and hormonal changes

Many people notice ulcers during a busy or stressful spell, after poor sleep or when they are run down. Stress does not cause every ulcer, but it can affect the body's ability to manage inflammation and may be a clear trigger for some people.

Hormonal changes can also play a part. Some women find ulcers are more common around their period. Keeping a brief note of when ulcers occur, alongside changes in sleep, stress and diet, can reveal a useful pattern over a few months.

Food and drink triggers

Acidic, salty, crunchy or spicy foods can irritate an existing ulcer, and certain foods may trigger new ones in susceptible people. Common examples include citrus fruit, pineapple, tomatoes, nuts, chocolate, coffee and strongly flavoured crisps. This does not mean everyone with ulcers needs to avoid these foods permanently.

The practical approach is to notice whether one food repeatedly appears before an outbreak. Avoid it for a few weeks, then discuss ongoing symptoms with a pharmacist, dentist or GP rather than cutting out a wide range of nutritious foods without advice.

Toothpaste and oral care products

Some people find that toothpaste containing sodium lauryl sulphate, often shortened to SLS, makes recurring ulcers more likely or more painful. SLS is a foaming agent found in many toothpastes. Switching to an SLS-free toothpaste is a straightforward trial and may be worthwhile if you get ulcers regularly.

If you are looking for an SLS-free option for your daily oral-care routine, explore Bioxtra Dry Mouth Mild Toothpaste 50ml X 3. This is a daily toothpaste, not a treatment for mouth ulcers. Check the ingredients and product directions before use.

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Choose a soft-bristled toothbrush and brush gently around sore areas. Alcohol-containing mouthwashes can sting and dry the mouth for some people, so they are not always the most comfortable option while an ulcer is active.

Low levels of key nutrients

Recurring mouth ulcers can occasionally be linked with low iron, vitamin B12, folate or zinc. These nutrients support healthy blood cells and tissues, so low levels may make the mouth lining more vulnerable.

This is more likely if you also feel unusually tired, look pale, become short of breath easily, have a restricted diet or have heavy periods. Rather than taking high-dose supplements at random, speak to a GP or pharmacist. A blood test may help identify whether there is a deficiency and what treatment is appropriate.

Medicines and underlying health conditions

Some medicines can contribute to mouth ulcers or a dry, sore mouth. This includes certain anti-inflammatory painkillers, beta blockers, medicines that affect the immune system and some treatments used for cancer. Do not stop prescribed medicine because of ulcers without speaking to the prescriber or a pharmacist first.

Less commonly, persistent or frequent ulcers can be associated with conditions such as coeliac disease, Crohn's disease, ulcerative colitis or Behçet's disease. Your GP may want to investigate if ulcers happen alongside digestive symptoms, joint pain, genital ulcers, skin rashes, eye inflammation or ongoing fatigue.

How to ease the pain while a mouth ulcer heals

Most uncomplicated ulcers heal on their own. The aim is to reduce pain, avoid further irritation and make eating and drinking manageable. Cool drinks and softer foods such as yoghurt, soup that has cooled, scrambled egg or mashed potato may be easier for a few days.

Avoid sharp, acidic and spicy foods until the area settles, and try not to touch the ulcer with your tongue. Gentle rinsing with warm salt water can be soothing for adults and older children who can rinse and spit safely. Mix half a teaspoon of salt into a glass of warm water, rinse gently, then spit it out.

A pharmacist can help you choose suitable over-the-counter options, including protective gels, pain-relieving sprays or mouthwashes designed for mouth ulcers. Some products contain ingredients that numb discomfort temporarily, while others help reduce irritation or support healing. Always check the label for age limits, directions and whether a product is suitable if you are pregnant, breastfeeding or taking regular medicines.

If ulcers are severe or keep returning, a GP or dentist may recommend a stronger treatment, such as a corticosteroid mouth treatment. These are not right for every cause of mouth soreness, which is why an assessment is useful before relying on them repeatedly.

When recurring mouth ulcers need medical advice

A single small ulcer that clears within two weeks is usually not a cause for alarm. Book an appointment with a dentist or GP if an ulcer lasts longer than three weeks, is unusually large, keeps bleeding or appears in the same place repeatedly.

You should also seek advice sooner if ulcers are making it difficult to eat or drink, you have a high temperature, swollen glands, weight loss, persistent diarrhoea or marked tiredness. For children, contact a GP or pharmacist if they are not drinking enough, seem unwell or have repeated painful ulcers.

A dentist can check for local causes such as tooth damage, sharp edges or dentures. A GP can consider wider causes, review medicines and arrange tests if needed. Getting a proper answer is especially helpful when ulcers have become a regular part of life rather than an occasional nuisance.

Reducing the chance of another outbreak

There is no guaranteed way to prevent every mouth ulcer, particularly when you are naturally prone to them. However, small changes can reduce avoidable irritation. Use a soft toothbrush, consider an SLS-free toothpaste, keep up regular dental checks and replace damaged toothbrushes. A balanced diet that includes sources of iron, B vitamins and folate supports general mouth health too.

It can also help to act early. If you recognise the first tingle or sore patch, switch to bland, softer meals for a day or two and use an appropriate pharmacy treatment before the area becomes more irritated. Keep a note of triggers, but do not let a few ulcers push you into overly restrictive eating.

If mouth ulcers keep disrupting meals, sleep or everyday comfort, do not simply put up with them. A pharmacist, dentist or GP can help you work out whether an everyday trigger, an oral care change or a health check is the most sensible next step.