Mouth Ulcers: Causes, Treatment and When to See Your Dentist

Mouth ulcers are one of the most common oral health conditions — uncomfortable enough to affect eating, drinking, and talking, but usually harmless and short-lived. Most people will have one at some point, and for many, they come back regularly without an obvious explanation.

This guide covers what causes them, how to manage them at home, and the signs that indicate a routine ulcer needs professional attention.

What Are Mouth Ulcers?

Mouth ulcers are small sores that develop on the soft tissue inside the mouth — the inner cheeks, gums, tongue, lips, or the floor of the mouth. They’re typically round or oval, with a white or yellow centre and a red border, and can range from a few millimetres to about a centimetre in diameter.

The most common type is the aphthous ulcer, also called a canker sore. These are not contagious and are not caused by a virus. Unlike mouth ulcers, cold sores form on the outside of the lips. This sets them apart from cold sores, which occur on the outer lip, are caused by the herpes simplex virus, and are contagious.

Most aphthous ulcers resolve naturally within one to two weeks.

What Causes Mouth Ulcers?

There’s often no single clear cause, and for many people they appear without an obvious trigger. That said, several factors are consistently associated with their development.

Minor injury

Biting the inside of the cheek, catching the gum with a toothbrush, or irritation from a sharp tooth or dental appliance are common physical triggers. The ulcer typically appears within a day or two of the injury.

Acidic or irritating foods

Citrus fruits, tomatoes, pineapple, and spicy foods can trigger ulcers in susceptible people or aggravate existing ones. Highly processed foods and those with sodium lauryl sulphate — a foaming agent found in some toothpastes — have also been linked to increased frequency in some patients.

Stress

There’s a well-established association between stress and aphthous ulcers, though the exact mechanism isn’t fully understood. Many patients notice they develop ulcers during periods of high stress or disrupted sleep.

Nutritional deficiencies

Deficiencies in vitamin B12, iron, or folate have been linked to recurrent mouth ulcers. If ulcers are frequent and no other cause is apparent, a blood test to check these levels is worth discussing with your GP.

Hormonal changes

Some people — particularly women — notice a pattern of ulcers appearing at certain points in the menstrual cycle. Ulcers during pregnancy are also common.

Medicines

Certain medicines, including non-steroidal anti-inflammatory drugs (NSAIDs), beta-blockers, and some chemotherapy agents, list mouth ulcers as a known side effect. If ulcers develop or their frequency increases after starting a new medicine, it’s worth flagging this to the prescribing doctor.

Underlying health conditions

In some cases, recurring mouth ulcers are associated with conditions such as coeliac disease, Crohn’s disease, or Behçet’s disease. These causes are uncommon but should be considered when ulcers are recurrent, severe, or associated with other symptoms.

What They Look Like and What to Expect

Most mouth ulcers follow a recognisable pattern. They start as a small red spot or tingling sensation, develop into an open sore within a day or so, and then gradually heal from the edges inward.

Minor aphthous ulcers — the most common type — are usually under a centimetre in diameter and appear one at a time, or occasionally in small clusters. They’re painful to touch and can make eating, drinking hot liquids, or brushing that area uncomfortable.

Major aphthous ulcers are less common, larger, and take longer to heal — sometimes several weeks. They may leave a small scar once healed.

Herpetiform ulcers are a less common type that appear as clusters of many small sores. Despite the name, they’re not caused by the herpes virus.

Home Care Tips

No treatment makes a mouth ulcer disappear overnight, but several measures reduce discomfort and support healing.

Saltwater rinse

Regular cleaning of the area (several times a day) with half a teaspoon of salt in a glass of warm water, in order to reduce inflammation and keep the area clean and discourage bacteria.

Over-the-counter gels and pastes

Topical anaesthetic gels — such as those containing benzocaine or lidocaine — numb the area temporarily and make eating and drinking more manageable. Protective pastes create a barrier over the ulcer to minimise irritation from food and saliva.

Avoid triggers

Acidic, spicy, and highly processed foods tend to aggravate ulcers and slow healing. Stick to soft, neutral foods while the ulcer is present. If a particular food consistently triggers ulcers, cutting it out is worth trying.

Toothpaste

If you’re prone to recurring ulcers, switching to a toothpaste that doesn’t contain sodium lauryl sulphate may reduce frequency. These are available at pharmacies and most health food stores.

What to avoid

Avoid scrubbing or attempting to pop a mouth ulcer, as this can delay healing and increase the risk of infection. Avoid alcohol-based mouthwashes, which can further irritate the tissue.

When to See a Dentist

Most mouth ulcers don’t need professional attention. Book an appointment if:

• An ulcer hasn’t healed after three weeks.
• You have an unusually large ulcer — larger than a centimetre.
• Ulcers are recurring frequently, with little time between episodes.
• You have multiple ulcers appearing at the same time regularly.
• Fever, swollen lymph nodes, or difficulty swallowing accompany the ulcer.
• An ulcer is painless — painless sores in the mouth can occasionally indicate a need for investigation.
• You have a sore that bleeds without being touched, has an irregular border, or appears on the floor of the mouth or under the tongue.

Any sore that doesn’t follow the usual pattern — especially one that persists beyond three weeks — should be assessed to rule out other causes, including oral cancer.

Frequently Asked Questions

Are mouth ulcers contagious?

Aphthous ulcers — the most common type — are not contagious. A virus does not cause them and can’t be passed on through contact. Cold sores are contagious and form on the outside of your lips due to the herpes simplex virus. If you’re unsure which you have, a dentist can clarify.

Why do I keep getting mouth ulcers?

Recurring ulcers are often linked to stress, nutritional deficiencies, hormonal changes, or certain foods. If ulcers are frequent and disruptive, a blood test to check B12, iron, and folate levels is a useful starting point. Persistent recurrence without an obvious cause is worth discussing with a dentist or GP.

How long does a mouth ulcer last?

Most minor aphthous ulcers heal within seven to fourteen days. Major ulcers can take longer — up to several weeks.

Can children get mouth ulcers?

Yes. Mouth ulcers are common in children and teenagers. The causes are similar to those in adults — minor injury, stress, certain foods. Management at home is the same: saltwater rinses, soft foods, and topical gels if needed. If a child has frequent or unusually large ulcers, it’s worth mentioning at their next dental check-up.

Is there anything that prevents mouth ulcers?

There’s no guaranteed prevention, but identifying and avoiding personal triggers — specific foods, toothpaste ingredients, stress — can reduce frequency. Maintaining adequate levels of B12, iron, and folate, particularly for people prone to recurrent ulcers, is also helpful.

Mouth Ulcers Management in Cabramatta

If you have a mouth ulcer that hasn’t healed after three weeks, keeps coming back, or doesn’t look like a typical ulcer, don’t leave it.

Call us on (02) 9755 5300 or book online.

Find us at 47 Arthur St, Cabramatta. At Cabramatta Dental Care, we see patients from Cabramatta, Canley Vale, Fairfield, Bonnyrigg, and Liverpool.