Mouth Ulcer Causes

What Are the Most Common Mouth Ulcer Causes?

Most mouth ulcer causes fall into two groups. First come minor injuries inside the mouth. Next come triggers such as stress or hormonal change. Experts suspect an immune overreaction, although the exact mechanism remains unclear. Genes matter too, because some families get ulcers more often.

Spotting a typical ulcer

Expect a shallow, round or oval sore with a pale centre and red rim. Most measure under a centimetre, yet even a tiny one stings with every mouthful.

Aphthous ulcer

The medical name for a common, non-infectious mouth ulcer with a pale base and a red border.

Minor aphthous ulcer

The usual form: under about 1 cm across and gone within roughly two weeks, without a scar.

Major aphthous ulcer

A larger, deeper ulcer that can take several weeks to heal and may leave a scar.

Recurrent aphthous stomatitis

A pattern of ulcers that keep returning, often several times a year.

Orthodontic wax

A soft, medicine-free wax pressed over a bracket or wire end to stop it rubbing the cheek.

Why Does the Same Spot Keep Getting Sore?

A bracket, a chipped tooth or a rough filling is usually rubbing it. The tissue never gets a break, so a scratch becomes an open sore. Among all mouth ulcer causes, these local ones are the easiest to fix. A dentist can often smooth an edge or adjust a wire. After that, the ulcer usually heals within days.

Braces and the first few weeks

During the first weeks, the inner cheeks and lips rub against metal edges all day. Wire adjustments can then bring back the soreness for a while. This is normal during orthodontic treatment with braces and settles with simple care. Prefer no brackets at all? Our guide to clear aligners vs braces compares both options.

A two-minute fix with orthodontic wax

First, roll a pea-sized piece of wax into a ball. Next, dry the bracket with a tissue so the wax sticks. Then press it over the sharp spot. Take it off before meals and add a fresh piece after brushing. A poking wire, however, needs trimming by your orthodontist.

Broken teeth, rough fillings and loose dentures

A chipped tooth or a rough filling edge can graze the tongue with every word. Similarly, a loose denture can rub a sore into the gum. These ulcers return until the edge changes. So a dentist can polish the surface or replace an old dental filling.

Could Stress or Your Toothpaste Be to Blame?

Yes to both, and hormones join the list of mouth ulcer causes. But these triggers mainly affect people who are already prone. The NHS names feeling tired, stressed or anxious as common triggers. Hormonal changes, for example during pregnancy, can make ulcers more frequent. How tension shows up as clenching and jaw ache is covered in our piece on stress and teeth grinding.

What to note in a food diary

Food is among the most personal causes of mouth ulcers. Some people react to nuts, strawberries, tomatoes, pineapple or hard cheese. There is no universal list, so keep a two-week diary. Note your toothpaste too, because its foaming agent, sodium lauryl sulphate, irritates some mouths.

Four small crossover trials compared toothpaste with and without sodium lauryl sulphate. Without it, ulcers healed about two days sooner on average. Sore counts and pain fell as well. However, none of the trials had a low risk of bias.

Alli BY, Erinoso OA, Olawuyi AB. Systematic review, Journal of Oral Pathology & Medicine, 2019.

Why Do I Keep Getting Mouth Ulcers?

Frequent ulcers usually reflect a mix of genes, stress and repeated minor injury. Still, ulcers that return every few weeks deserve a closer look. Some mouth ulcer causes only show up on a blood test, such as low iron, vitamin B12 or folate. Less often, coeliac disease, Crohn’s disease or Behçet’s disease first appears as recurring mouth sores.

Vitamins, minerals and medicines

The NHS lists low iron, zinc, folic acid, vitamin B and vitamin D as possible triggers. Your GP can arrange a blood test, so avoid guessing with supplements. Some anti-inflammatory painkillers and beta blockers can trigger ulcers too. Even so, never stop a medicine without asking your prescriber.

Gut, skin and joint symptoms

Ulcers with ongoing diarrhoea, tummy pain or weight loss call for a GP and possibly a gastroenterologist. Sores on the skin or genitals, or painful swollen joints, matter too. Then a rheumatologist or dermatologist should assess you. In short, only a specialist can make that diagnosis.

Is It a Mouth Ulcer or a Cold Sore?

Location and cause are the quickest clues. A cold sore comes from the herpes simplex virus, so it spreads easily. It usually starts with tingling, then blisters around the lips. By contrast, a mouth ulcer sits inside the mouth and cannot pass to anyone else. Kissing, for example, can spread a cold sore but never appears among mouth ulcer causes.

What Actually Soothes a Mouth Ulcer?

The NHS says most ulcers clear up by themselves within a week or two. There is no instant cure, so the goal is comfort and protection. Whichever mouth ulcer causes apply to you, the same gentle routine helps. If pain still disturbs eating or sleep, ask a pharmacist for advice.

1. Rinse with warm salt water a few times a day.
2. Choose soft, lukewarm or cool food until the sore settles.
3. Skip spicy, salty, acidic and crunchy food for now.
4. Sip cold drinks through a straw so they bypass the ulcer.
5. Brush gently with a soft-bristled toothbrush after meals.
6. Try a toothpaste without sodium lauryl sulphate for a few weeks.
7. Keep orthodontic wax on any rubbing bracket, then refresh it after meals.

Pharmacy options worth knowing

Pharmacists can suggest numbing gels, protective pastes and antimicrobial or salt mouthwashes. Use them briefly and follow the leaflet. For children or during pregnancy, check the choice with the pharmacist first. Severe ulcers may need a prescription from your dentist instead.

When Should a Mouth Ulcer Worry You?

See a dentist or GP about any ulcer lasting beyond three weeks, as the NHS advises. Act sooner if a sore grows unusually large, sits near the throat or keeps coming back. Bleeding, spreading redness or rising pain can signal infection, so call promptly. Finally, never ignore a painless patch that feels hard.

Why painless sores matter

A typical ulcer hurts and starts shrinking within days. By contrast, a painless sore with raised or firm edges needs a closer look. Dentists look for this at routine visits; it is a standard part of mouth cancer screening. Then use the same visit to ask about repeat mouth ulcer causes. If your gums bleed instead of ulcerating, see our page on bleeding gums.