Mouth Ulcers That Won’t Heal? Here’s When to Worry + How to Get Relief

By Dr. Luke Kale · Medically reviewed by Dr. Reji Moideen · 07/04/2026 · Mouth Ulcers

A mouth ulcer that won’t heal after two to three weeks is the one warning sign you should never wait out, because most harmless canker sores clear on their own within 10 to 14 days. If a sore stays put longer than that, keeps growing, sits in the same spot, or turns painless and firm, it needs to be checked by a dentist. The good news is that the vast majority of mouth ulcers are benign, and simple care at home settles them quickly. This guide walks you through what causes them, when to worry, and how to get real relief.

Medically reviewed by Dr. Noha, General Dentist at Mint Dental Care, Dubai.

Mouth ulcers, also called canker sores, are small, tender lesions that form on the soft tissue inside your mouth or at the base of your gums. They can make eating, drinking, and even talking uncomfortable for a few days. If your family tends to get them, you’re more likely to get them too. At Mint Dental Care we see these sores every week, and patients are usually relieved to learn that the fix is often straightforward once the trigger is identified.

What causes mouth ulcers that won’t heal?

Most stubborn mouth ulcers come from ongoing irritation, an unresolved nutritional gap, or an underlying condition that keeps re-triggering the sore. Ordinary canker sores heal fast, so when one lingers it usually means something is still aggravating the tissue. Common triggers include:

Minor injuries, such as biting your cheek, a slip while brushing, or a toothbrush that’s too firm.
A sharp filling, a chipped tooth, or an edge that rubs the same spot with every bite.
Braces, aligners, or dentures pressing against the soft tissue.
Burns from hot food or irritation from strong, high-alcohol mouthwash.
Hormonal changes, stress, illness, or being run down.
Nutritional shortfalls in vitamin B2, folate, vitamin B12, or iron.
Viral infections, including the cold sore (herpes simplex) virus.
Reactions to certain medications.
Autoimmune and inflammatory conditions such as lichen planus.
Gut-related conditions such as coeliac disease or Crohn’s disease.

Recurring sores often point to more than one factor at once. Stress and fatigue lower your defences, and a rough tooth edge finishes the job. If your ulcers keep returning in cycles, it’s worth looking at how stress shows up in your mouth alongside any physical irritant, because calming one without fixing the other rarely works.

Mouth Ulcers That Won’t Heal? Here’s When to Worry + How to Get Relief at Mint Dental

Does a vitamin B2 deficiency cause oral ulcers?

Yes, a vitamin B2 (riboflavin) deficiency can cause oral ulcers, along with cracks at the corners of the mouth, a sore or swollen tongue, and inflamed lips. Riboflavin helps keep the lining of your mouth healthy, so when levels drop, the tissue becomes fragile and slow to repair. It rarely acts alone. Low folate, vitamin B12, and iron cause very similar sores, which is why persistent or recurring ulcers are sometimes the first visible clue to a deficiency you didn’t know you had.

If your diet is limited, you follow a strict vegan pattern, or you have a condition that affects how you absorb nutrients, a simple blood test can confirm whether a deficiency is behind the problem. Correcting the shortfall through diet or supplements often stops the ulcers from coming back. The mouth is a surprisingly honest messenger about what’s happening elsewhere in the body, and the signs a dentist can spot beyond your mouth frequently start with recurring sores like these.

Which nutrients matter most for healthy oral tissue?

Vitamin B2 (riboflavin): found in dairy, eggs, lean meat, and leafy greens.
Folate and vitamin B12: found in legumes, fortified cereals, fish, and poultry.
Iron: found in red meat, lentils, spinach, and fortified foods.

What are the symptoms of a mouth ulcer?

A typical mouth ulcer is a round or oval sore with a white, yellow, or grey centre and a red, inflamed border. It appears on the inner cheeks, lips, tongue, or the floor and roof of the mouth. Depending on the cause, you might notice:

One or several painful sores that sting when you eat or drink.
Heightened sensitivity to sour, spicy, or salty food.
Discomfort while brushing near the sore.
Swollen, red tissue surrounding the lesion.

One detail is easy to miss. A sore that doesn’t hurt is not always reassuring. A painless ulcer that refuses to heal is exactly the type that deserves a professional look, since some serious conditions, including oral cancer, can present without pain. Your tongue in particular can flag early trouble, and the clues your tongue reveals about your oral health are worth learning to read.

When should you worry about a mouth ulcer?

You should worry, and book an appointment, when a mouth ulcer lasts longer than three weeks, keeps growing, or comes back in the same place. Most sores are harmless, but a small number signal something that needs treatment. See a dentist or doctor if any of these apply:

The ulcer hasn’t healed after two to three weeks.
It’s unusually large or keeps getting bigger.
It’s painless, firm, or bleeds easily.
New ulcers appear before the older ones heal.
You also have a fever, swollen glands, or diarrhoea.
Swallowing, drinking, or eating has become very difficult.
The pain isn’t relieved by over-the-counter gels or painkillers.
Sores spread to your lips or the back of your throat.

Persistent mouth sores are sometimes tied to what’s happening in your digestive system, so if you also have ongoing stomach or bowel symptoms, it’s worth understanding how dental health links to digestive and gut issues. A dentist can connect the dots between your mouth and the rest of your body faster than you might expect.

How can you treat a mouth ulcer and get relief fast?

Most mouth ulcers heal on their own, and the goal of home care is to ease pain and speed recovery while the tissue repairs. Simple steps make a real difference:

Rinse gently with a warm salt-water or baking-soda solution a few times a day.
Use a toothpaste free of sodium lauryl sulfate (SLS), which irritates many people’s sores.
Apply a pharmacy pain-relieving gel or a protective mouth rinse directly to the sore.
Switch to a soft-bristled toothbrush and brush carefully around the area.
Avoid acidic, spicy, salty, and very hot foods until it settles.
Skip strong, high-alcohol mouthwash while the ulcer is active.

Why Regular Dental Check-ups Are Crucial for Oral Health in Dubai

If a sore is caused by a sharp tooth edge, a loose filling, or a rubbing denture or aligner, home care alone won’t fix it. The irritant has to be smoothed or adjusted, which takes a few minutes in the chair. This is one reason a routine dental check-up matters so much. A dentist can catch and correct the physical cause before it turns a two-week nuisance into a two-month problem.

How can you prevent mouth ulcers from coming back?

Prevention comes down to removing the triggers you can control. Eat a balanced diet rich in B vitamins, folate, and iron. Manage stress and sleep, since fatigue is a common trigger. Brush gently, replace a frayed toothbrush, and keep up with your regular dental visits so that any rough edges or ill-fitting appliances are fixed early.

When should you contact Mint Dental Care?

Get in touch with our team in Dubai whenever a mouth ulcer feels different from the usual few-day sore. We understand how much a persistent ulcer interferes with eating and speaking, and finding the real cause is the fastest route to lasting comfort. Reach out if:

Your ulcer still hasn’t healed after three weeks.
You keep getting several ulcers, or they return again and again.
A sore is bleeding, unusually large, or intensely painful.
You suspect a dental cause, such as a sharp filling, a rubbing brace, or a denture that doesn’t fit well.

Rather than covering the pain with a temporary fix, our dentists focus on the underlying reason your ulcers keep appearing, then tailor treatment to it. That might mean smoothing a tooth, adjusting an appliance, checking for a deficiency, or referring you for further tests when needed. You don’t have to live with recurring discomfort.

Frequently Asked Questions

Does a vitamin B2 deficiency cause oral ulcers?

Yes. A shortage of vitamin B2 (riboflavin) can trigger mouth ulcers, cracked lips, and a sore tongue because riboflavin helps maintain the lining of the mouth. Low folate, B12, and iron cause similar sores, so a blood test is the best way to confirm the cause and correct it.

How long should a mouth ulcer take to heal?

A typical canker sore heals within 10 to 14 days without scarring. If a sore lasts longer than three weeks, gets bigger, or returns to the same spot, have it examined rather than waiting it out.

Can stress cause mouth ulcers?

Yes. Stress and fatigue weaken the body’s defences and are among the most common triggers for recurring canker sores. Many people notice ulcers flare during exams, deadlines, or periods of poor sleep.

Why do I keep getting mouth ulcers in the same place?

An ulcer that returns to the exact same spot is usually caused by a persistent physical irritant, such as a sharp tooth, a rough filling, or a rubbing denture or brace. A dentist can smooth or adjust the source so the sore can finally heal.

Is a painless mouth ulcer something to worry about?

A painless sore that refuses to heal deserves a professional check. While most ulcers are harmless, some serious conditions can appear without pain, so a persistent, painless, or firm ulcer should be assessed promptly.