Mouth Ulcers: Causes, Treatment and When to Worry

By the team at Bollington Dental Practice, under the clinical direction of Dr Ellie Burrows, Principal Dentist. Updated August 2026.

Almost everyone gets a mouth ulcer sooner or later, and for something so small they are remarkably good at ruining a week. Eating stings, talking rubs, and toothpaste suddenly feels like an aggressive substance. The reassuring truth is that the overwhelming majority of mouth ulcers are harmless and heal by themselves. The important truth is that a small minority are not, and there is one simple rule that separates the two.

The short answer

Most mouth ulcers heal on their own within one to two weeks. Warm salt water rinses, an over-the-counter protective gel from the pharmacy, and avoiding whatever is rubbing or stinging will get you through the healing time more comfortably. Nothing makes an ulcer vanish overnight, whatever the packaging promises.

The rule that matters: any mouth ulcer that has not healed after three weeks needs to be looked at by a dentist or doctor. Not because it is probably serious, but because a persistent ulcer is one of the earliest signs of mouth cancer, and the earlier that possibility is ruled out or caught, the better every outcome is. Our guide to the signs of mouth cancer covers this in more detail.

What causes mouth ulcers

Single ulcers usually have a mechanical cause, while crops of recurring ulcers tend to come from somewhere else. The common culprits:

Minor injury. A bitten cheek, a scratch from a sharp tooth or a broken filling, a toothbrush slip, braces or a denture rubbing, even a burn from food that was too hot. These ulcers appear at the site of the damage and heal once the cause is dealt with. If a sharp tooth or rough filling keeps catching the same spot, that needs smoothing by a dentist rather than enduring, because a wound that is constantly re-injured cannot heal.

Stress and tiredness. One of the most common triggers for recurrent ulcers, and often the explanation when they arrive in clusters during exams, work crunches or poor sleep.

Certain foods. Chocolate, coffee, strawberries, almonds, cheese and spicy or acidic foods trigger ulcers in some people. If yours recur, it is worth keeping a short diary to spot a pattern.

Sodium lauryl sulphate (SLS). A foaming agent in many toothpastes that is linked to more frequent ulcers in some people. Switching to an SLS-free toothpaste is a cheap experiment that genuinely helps some recurrent sufferers.

Vitamin and mineral deficiencies. Low vitamin B12, iron or folate can show up as recurring mouth ulcers. This is one reason a pattern of frequent ulcers deserves a conversation with your GP rather than a lifetime supply of gel.

Hormonal changes, stopping smoking, and some medications can all trigger ulcers. Ulcers that start after a new medication are worth mentioning to whoever prescribed it.

Underlying conditions. Recurring crops of ulcers are occasionally linked to conditions such as coeliac disease, Crohn’s disease or Behçet’s disease. Rare, but part of why “I just always get ulcers” should be investigated once rather than accepted forever.

What actually helps one heal

Warm salt water rinses. Half a teaspoon of salt in a glass of warm water, several times a day. Unfashionable and effective at keeping the area clean while it heals.

A protective gel or paste from the pharmacy. Products that form a layer over the ulcer take the sting out of eating. Antimicrobial mouthwashes such as chlorhexidine can help prevent infection in the meantime. Your pharmacist can point you to the right shelf, and none of it needs a prescription.

Avoid what hurts. Spicy, acidic, salty and rough-textured foods will remind you they exist. A soft diet and a straw for acidic drinks make the healing week far more bearable.

Deal with the cause. If the ulcer sits exactly where a sharp tooth, filling edge or denture catches, treating the ulcer without fixing the snag is a loop. Smoothing a sharp edge is quick, and a denture that rubs needs adjusting, not tolerating.

What does not help: dabbing ulcers with neat salt, aspirin held against the gum, or any of the folklore remedies that add a chemical burn to an existing wound. Enamel and soft tissue do not benefit from being attacked.

Do you see a dentist or a doctor, and what does it cost?

For an ulcer clearly caused by a tooth, filling or denture, a dentist is the right call, because the fix is dental. For recurring crops of ulcers with no obvious dental cause, your GP is often the better starting point, since blood tests for deficiencies and underlying conditions sit on their side of the fence. For the three-week rule, either professional can look, and neither should be put off.

At Bollington Dental Practice, checking a persistent ulcer is part of an examination. For new patients that is £89 including X-rays, and existing patients can book a check-up in the usual way. If something needs smoothing or adjusting to let an ulcer heal, we will tell you exactly what it costs before anything is done, and our prices are published on our fees page. Every routine examination here also includes a soft tissue check of your tongue, cheeks and gums, which is precisely how persistent problems get spotted early.

In pain right now? Our two-minute urgency checker tells you honestly whether this is a call-us-today problem or one that can wait, with practical advice in the meantime.

Frequently asked questions

How long should a mouth ulcer take to heal?

Most heal within one to two weeks without any treatment. Larger ulcers can take a little longer and occasionally leave a small scar. Anything still there at three weeks needs a professional look, even if it does not hurt. Painless and persistent is actually the combination to take most seriously, not least.

Why do I keep getting mouth ulcers?

Recurrent ulcers are most often linked to stress, tiredness, minor trauma from brushing or biting, certain foods, or the foaming agent SLS in some toothpastes. Less commonly they point to low B12, iron or folate, or an underlying condition. If you get them frequently, it is worth one proper conversation with your dentist and GP rather than years of just coping.

What gets rid of a mouth ulcer fast?

Nothing removes one overnight, honestly. Salt water rinses, a protective pharmacy gel and avoiding trigger foods make the healing days comfortable, and treating any physical cause such as a sharp tooth stops the cycle. Anything promising instant cures is overpromising.

When should I worry about a mouth ulcer?

See a dentist or doctor promptly if an ulcer lasts more than three weeks, keeps coming back in the same spot, grows, bleeds without reason, or if you notice a lump, numbness or white or red patches alongside it. Most of the time the explanation is innocent, and the rare times it is not, being seen early makes a real difference.

Got an ulcer that will not heal?

Three weeks is the line. If yours has passed it, call us on 01625 574609 and we will take a proper look. New patients are welcome, an examination is £89 including X-rays, and all our prices are on our fees page.

Back to Blog