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

Most people know the feeling — a small sore appears in the mouth, eating becomes uncomfortable, and for a week or two, anything acidic or spicy is off the menu. Mouth ulcers are extremely common, usually harmless, and resolve on their own. But for some people, they come back repeatedly, and occasionally they signal a need for professional attention.

Here’s what causes them, how to manage the discomfort, and when a mouth ulcer is worth getting checked.

What Are Mouth Ulcers?

Mouth ulcers are open sores that form on the soft parts inside your mouth, including your cheeks, gums, tongue, lips, and the floor of your mouth. They’re typically round or oval with a white or yellow centre and a red border, and range in size from a few millimetres up to around a centimetre.

The most common type is the aphthous ulcer, also called a canker sore. A virus doesn’t cause mouth ulcers and can’t be passed from one person to another. This makes them different from cold sores, which appear on the outside of the lips; the herpes simplex virus causes cold sores.

Most aphthous ulcers are minor and heal without treatment within one to two weeks. A small proportion are larger or appear in clusters, take longer to heal, and cause more significant discomfort.

What Causes Mouth Ulcers?

For many people, ulcers appear without a clear trigger. But several factors are consistently linked to their development.

Minor injury

The most straightforward cause. Biting the inside of the cheek, catching the gum with a toothbrush, or irritation from a sharp tooth edge or dental appliance can all produce an ulcer within a day or two. These tend to be one-off occurrences in a specific location.

Acidic and spicy foods

Citrus fruits, tomatoes, pineapple, and spicy foods are common triggers for people prone to ulcers. They can both initiate new ulcers and significantly worsen existing ones. Highly processed foods and toothpastes containing sodium lauryl sulphate have also been associated with increased frequency in some patients.

Stress

The relationship between stress and mouth ulcers is well established. Many patients notice ulcers appearing consistently during periods of high stress, illness, or disrupted sleep — suggesting an immune component, though the exact mechanism isn’t fully understood.

Nutritional deficiencies

Recurring mouth ulcers can sometimes be caused by low levels of vitamin B12, iron, or folate—something that’s often overlooked. If ulcers keep coming back without an obvious trigger, a blood test to check these levels is a reasonable starting point — and one worth raising with a GP.

Hormonal changes

Some women notice that their mouth ulcers seem to appear at the same point in their menstrual cycle, suggesting that hormonal changes may be a trigger. Ulcers are also common during pregnancy as hormone levels shift.

Medicines

Non-steroidal anti-inflammatory drugs, beta-blockers, and certain chemotherapy agents can trigger mouth ulcers as a side effect. If ulcers began or became more frequent after starting a new medicine, it’s worth flagging with the prescribing doctor.

Underlying health conditions

For patients with frequent, severe, or unusually persistent ulcers, an underlying condition may be contributing. Coeliac disease, Crohn’s disease, and Behçet’s disease are all associated with recurrent oral ulceration. These are worth considering when ulcers don’t follow the typical pattern.

What They Look Like and What to Expect

A typical minor aphthous ulcer starts as a tingling or burning sensation, develops into an open sore within a day, and heals gradually over the following week to two weeks. The pain tends to be sharpest in the first few days and eases as healing progresses.

Minor ulcers are usually small — under a centimetre — and appear one at a time, though small clusters are possible. They’re painful when touched by food or drink, and sometimes even when simply talking.

Major aphthous ulcers are less common. They’re larger and deeper, take longer to heal — sometimes several weeks — and may leave a small scar. Herpetiform ulcers appear as clusters of many small sores and, despite the name, are not related to the herpes virus.

Home Care: What Helps and What Doesn’t

No treatment dramatically speeds up healing, but several measures can reduce discomfort and keep the area clean while the ulcer heals.

Saltwater rinse

It is important to rinse off the site several times a day for 30 to 60 seconds with half a teaspoon of warm water containing salt to help keep the sore area clean, to eliminate inflammation and to decrease the amount of bacteria around the sore. It stings initially but settles quickly.

Over-the-counter gels and pastes

Topical anaesthetic gels containing benzocaine or lidocaine numb the area and make eating and drinking more manageable. Barrier pastes adhere to the ulcer surface and protect it from further irritation. Both are available at pharmacies without a prescription.

Avoid triggers

Acidic, spicy, and highly processed foods slow healing and increase pain. Soft, neutral foods are easier to manage while an ulcer is present. If certain foods consistently trigger ulcers, removing them is worth trying.

Toothpaste

Switching to a toothpaste without sodium lauryl sulphate may reduce the frequency of ulcers in patients who are prone to them. You can find these at most pharmacies and health food stores.

What doesn’t help

Trying to scrub or burst the ulcer delays healing and increases the risk of secondary infection. Alcohol-based mouthwashes irritate the tissue and should be avoided while an ulcer is present.

When to See a Dentist

Most mouth ulcers don’t need professional attention. See your Gordon dentist if:

• An ulcer hasn’t healed after three weeks.
• It’s unusually large — more than a centimetre across
• You’re getting ulcers very frequently, with little recovery time between episodes.
• Multiple ulcers are appearing simultaneously regularly.
• Fever, swollen lymph nodes, or difficulty swallowing accompany the ulcer.
• A sore is painless — painless ulcers are less typical and worth assessing.
• You have a sore that bleeds without contact, has an irregular border, or sits on the floor of the mouth or under the tongue.

Any sore that persists beyond three weeks, doesn’t follow the usual pattern, or appears in an unusual location should be assessed to rule out other causes — including oral cancer.

Frequently Asked Questions

Are mouth ulcers contagious?

Aphthous ulcers — canker sores — are not contagious. A virus does not cause them and can’t be spread through contact. Cold sores are contagious, but they appear on the outer lip rather than inside the mouth. If you’re not sure which you have, a dentist can tell the difference quickly.

Why do I keep getting mouth ulcers?

Recurring ulcers are common and often linked to stress, diet, hormonal changes, or nutritional deficiencies. If they’re frequent and disruptive, checking B12, iron, and folate levels is a useful starting point. Persistent recurrence without an obvious cause — particularly if ulcers are severe or slow to heal — warrants a dental or GP review to rule out an underlying condition.

How long should a mouth ulcer take to heal?

Minor ulcers typically resolve within seven to fourteen days. Major ulcers can take several weeks. Any ulcer that hasn’t healed within three weeks should be assessed by a professional.

Can children get mouth ulcers?

Yes — ulcers are common in children and teenagers, and the causes are similar to those in adults. Home management is the same: saltwater rinses, soft foods, and topical gels as needed. Frequent or unusually large ulcers in children are worth raising at a dental check-up.

Is there anything that prevents them?

There’s no guaranteed prevention, but identifying personal triggers — specific foods, toothpaste ingredients, stress — and avoiding them can reduce the frequency for many people. Maintaining adequate levels of B12, iron, and folate also helps patients with deficiencies.

Mouth Ulcers Management in Gordon

If you have a mouth ulcer that hasn’t healed after three weeks, keeps coming back, or doesn’t look like a typical ulcer, get it checked sooner rather than later.

Call us on (02) 9498 8290 or book online.

We’re at Suite 3, 2 St Johns Ave in Gordon. We see patients from Gordon, Pymble, Killara, St Ives, and Turramurra.