Mouth Ulcers

A sore in your mouth: is it a mouth ulcer, or something else?

Where the sore sits, how long it lasts and whether it comes back: the three questions that tell them apart

A small sore that appears in your mouth is most often a mouth ulcer: painful but self-limiting, a tissue reaction almost everyone comes across at least once in their life. But the same appearance can also come from a spot where a denture or a brace keeps pressing, a mark left by a hard-bristled brush or biting your cheek; rarely, a single sore that lasts longer than three weeks can be a sign of something else. This page explains the tell-tale look of a mouth ulcer, how to tell it apart from a sore caused by a denture or a brace, and what actually helps at home.

Short answer

A single mouth sore is most often a mouth ulcer: it appears on moving parts of the mucosa, such as inside the cheek, inside the lip or under the tongue, with a yellow-grey centre, a red border, and pain that usually clears within one to two weeks. The same look can also come from a pressure sore where a denture or brace edge keeps pressing; it improves within days once you remove the appliance. The exact cause is unknown, but mouth ulcers are linked to minor trauma, acidic or spicy food, stress and certain vitamin deficiencies. A sore lasting over three weeks or recurring in the same spot needs checking.

The usual course of a mouth ulcer: Clears on its own within one to two weeks
When to see a dentist: A single sore that lasts longer than three weeks
Often mistaken for a mouth ulcer: A rubbing sore from a denture or brace
What tells them apart: Whether it is a fixed spot, and whether it heals without the appliance

Mouth ulcer, rubbing sore, or something else

A sore that appears in the mouth can actually be the shared appearance of several different conditions. The most common is a mouth ulcer; next comes a spot that a denture, a brace or a broken tooth keeps rubbing; more rarely, it can be an infection or a tissue change that has not healed for a long time. We tell them apart by looking at where the sore sits, how long it lasts and whether it keeps coming back.

A mouth ulcer has a look of its own: round or oval, with a centre somewhere between yellow and grey, surrounded by a red border, and painful to the touch. It appears on the moving parts of the mucosa, such as inside the cheek, inside the lip, under the tongue or the soft palate; it is rarely seen on the firm, fixed part of the gum. It can appear on its own or several at once.

The exact cause of mouth ulcers is not fully known. Minor trauma in the mouth, such as accidentally biting your cheek, a hard-bristled brush or a dental brace, acidic or spicy food, stress and the foaming agents in some toothpastes are known triggers. Some people who get mouth ulcers often turn out to have low iron, B12 or folic acid levels; this link is not the cause of the ulcer on its own, but a possibility worth investigating.

Mistaking a rubbing sore from a denture or a brace for a mouth ulcer is a common error, though telling them apart is easy. This sore always forms in the same spot, where the appliance presses; if you take the appliance out and rest the area for a while, it noticeably shrinks within a few days. A mouth ulcer, on the other hand, has nothing to do with an appliance: it appears on its own on a moving part of the mucosa and does not change when you take the appliance out.

Duration is the most practical measure that separates a mouth ulcer from the other possibilities. Most mouth ulcers shrink and disappear within one to two weeks; a single sore that lasts longer than three weeks and does not close in the same spot does not fit the usual course of a mouth ulcer and needs to be seen by a dentist or doctor. A sore that keeps coming back in the same area again and again should not be dismissed as just a mouth ulcer either.

The most common mistake at home is carrying on wearing an appliance that is causing irritation and waiting for the sore to harden on its own. A sore caused by a denture or a brace does not clear without taking the appliance out or having it adjusted; pressure on the same spot for days on end can turn into permanent irritation in the tissue.

Another common mistake is trying different toothpastes and mouthwashes one after another. Products with a strong flavour or foaming agents can irritate the mucosa further, delaying healing rather than clearing the ulcer. A painkiller tablet applied directly to the sore increases irritation in the tissue in the same way.

Does the appearance point to a mouth ulcer, or to an appliance?

The points on the left show the typical course of a mouth ulcer; those on the right show a sore caused by an appliance, or a condition that needs seeing a dentist.

The tooth can be saved

The sore is round, with a yellow-grey centre and a red borderThis is the typical look of a mouth ulcer. The pain is usually most intense in the first few days, then eases gradually.
It is inside the cheek, inside the lip or under the tongueMouth ulcers appear on the moving parts of the mucosa. If a sore keeps coming back on the firm, fixed part of the gum, another cause should be looked for.
It is shrinking within one to two weeksMost mouth ulcers ease on their own within this time. The longer it goes on, the less likely it is a mouth ulcer, and another cause should be investigated.
It appeared right after a bite or dental treatmentA single sore that appears right after minor trauma usually clears along with its cause, and has nothing to do with an appliance or with recurrence.

Saving it is unlikely to hold

If it is at a fixed spot where the edge of a denture or brace pressesA sore that keeps appearing in the same spot is not a mouth ulcer; it is pressure from the appliance. It improves within a few days once you take the appliance out or your dentist adjusts it; if it does not, the adjustment needs repeating.
If it has lasted longer than three weeks and is not closingThis is beyond the usual course of a mouth ulcer. Because it can rarely be a sign of something more serious, it needs to be checked.
If it keeps coming back in the same areaFor a recurring sore, an underlying trigger, such as an appliance, a broken tooth or a recurring vitamin deficiency, should be investigated.
If it is painless, hard-edged and growingA mouth ulcer is usually painful and shrinks over time. A sore that is painless, growing or hardening does not fit the typical course of a mouth ulcer and must be assessed.

How your dentist assesses the sore

For a sore that keeps coming back or lasts a long time, the place to go is your dentist or your doctor; this page does not replace that visit.

1
The history
You are asked when the sore appeared, whether it is a first occurrence or a repeat, whether you wear a denture or a brace, your eating habits and whether you are going through a stressful period.
2
Visual examination
The shape, location, border and colour of the sore largely tell a mouth ulcer apart from a sore caused by an appliance.
3
Denture or brace check
If you wear an appliance, the pressure points are checked; if the sore is coming from here, this is corrected before looking for a problem with the teeth or with vitamins.
4
A referral for blood tests for recurring mouth ulcers
Patients who get mouth ulcers frequently may be referred to their doctor for iron, B12 and folic acid levels; if a deficiency is found, treating it can reduce how often they come back.
5
Further assessment for a sore lasting longer than three weeks
For a sore that does not fit the usual course of a mouth ulcer and does not close, further assessment, including a biopsy, may be needed. This step should not be skipped.

What is done, depending on the source

Treatment differs between a mouth ulcer and a sore caused by an appliance; below is what applies to each.

Mouth ulcer: soothing care

Rinsing with salt water, staying away from hot, spicy and acidic food for a while and using a soft-bristled brush make healing easier. Your pharmacist may recommend a gel or a mouthwash that eases the pain; follow the patient information leaflet on the product for how long to use it.

A sore caused by a denture or brace: adjustment

The spot where the appliance presses is carefully thinned down by your dentist, or that part of the brace is changed. Dealing with it yourself moves the pressure point but does not solve it.

Recurring mouth ulcers: investigating a deficiency

In patients who get mouth ulcers frequently, iron, B12 and folic acid levels can be checked. If a deficiency is found, treatment is planned by your doctor.

A sore that will not heal: further assessment

For a sore that lasts longer than three weeks or does not fit the typical look of a mouth ulcer, further investigation, including a biopsy, may be needed; there is no benefit in putting this step off and waiting.

A chronic denture sore: a fixed alternative

If a denture keeps irritating the same spot, the sore does not close, and even when it does, it keeps coming back in the same place. We cover this in detail on our denture sore page. For patients with many missing teeth who keep getting sores from a denture, in the protocol we use, the teeth are fixed to implants, so there is no base resting on the gum; this is a separate option that removes the source of the denture sore.

What putting it off changes

The points below show what you actually lose by putting off the sore.

A rubbing sore can become permanent alongside the appliance

Ignoring a sore caused by a denture or a brace and carrying on wearing the appliance can lead to permanent irritation in the tissue; beyond this point, a simple adjustment may not be enough.

Continuing to eat spicy and acidic food delays healing

If the sore keeps being irritated by the same foods while it is healing, it takes longer. During this time, also pay attention to what is in your mouthwash and rinses; products with a strong flavour can increase irritation.

Assuming a sore that has lasted more than three weeks is just a mouth ulcer and waiting

The usual course of a mouth ulcer does not go beyond this length of time. The longer it goes on, the more time that an early check-up could have saved is lost.

Trying different products one after another to speed up healing

Giving up one mouthwash for another, then trying a gel and abandoning that too, makes it harder for the sore to follow its own course. Ask your pharmacist which product is recommended and stick with it.

When the sore goes away

The timeline differs between a mouth ulcer and a sore caused by an appliance.

The first few days
The most painful period of a mouth ulcer is usually the start; it is felt while eating and talking.
One week
Most mouth ulcers start to shrink and become less painful within this time.
Two weeks
Most mouth ulcers close completely within this time. If it has not closed, it has moved outside the usual course of a mouth ulcer.
A few days after an appliance adjustment
A sore caused by a denture or a brace usually improves noticeably within a few days once the pressure is removed.

Message us right away if

The sore has lasted more than three weeks. This is beyond the usual limit for a mouth ulcer; it needs to be checked.
It keeps coming back in the same spot. For a recurring sore, an underlying cause should be investigated.
Fever, difficulty swallowing or weight loss along with the sore. These signs suggest the problem may not be confined to the mouth; it should be assessed without delay.
The same spot is not improving despite a denture adjustment. The adjustment may not have been enough; see your dentist again.

What affects the cost

Because most mouth ulcers clear on their own without any treatment, the cost is usually about adjusting an appliance or investigating a recurring sore. These are the items that determine the scope:

Whether the sore is related to an appliance: A mouth ulcer usually carries no extra cost; adjusting a denture or a brace needs a separate appointment and procedure.
Whether blood tests are needed: Iron, B12 and folic acid tests requested for recurring mouth ulcers fall under your doctor's remit, not your dentist's.
Whether further assessment is needed: A biopsy or further investigation needed for a sore lasting longer than three weeks changes the scope and the timescale.
Whether the source is a denture: Whether an old denture that keeps causing sores needs to be remade is a separate item.

Frequently asked questions

Are mouth ulcers contagious?

No. Unlike a cold sore, a mouth ulcer is not caused by a virus and does not pass from one person to another. This is one of the key differences that tells it apart from cold sores in the mouth.

Why do mouth ulcers keep coming back?

The exact cause is not fully known, but minor trauma, stress, acidic or spicy food and certain vitamin deficiencies are known triggers. If they keep coming back often, checking your iron, B12 and folic acid levels can be worthwhile.

Is the spot where my denture presses a mouth ulcer?

Probably not. A mouth ulcer appears on its own on a moving part of the mucosa; a sore where a denture presses always forms at the same spot and improves within a few days once you take the denture out. If it does not improve, the denture needs adjusting.

What can I do at home for a mouth ulcer?

Rinsing with salt water, staying away from hot, spicy and acidic food for a while and using a soft-bristled brush are soothing. If the pain carries on, you can ask your pharmacist to recommend a gel or a mouthwash.

Is it all right to put a painkiller tablet directly on a mouth ulcer?

We do not recommend it; when the tablet touches the tissue directly, it can increase irritation. Painkillers are made to be swallowed; follow the patient information leaflet for how to use them, or ask your pharmacist.

Are mouth ulcers and cold sores the same thing?

No. A cold sore is caused by a virus, is contagious and usually appears on the outer edge of the lip. A mouth ulcer is seen inside the mouth, on the moving parts of the mucosa, and is not contagious.

My sore has lasted more than three weeks and the pain has eased. Should I still see a dentist?

Yes. Less pain does not mean it is healing; a sore that lasts longer than three weeks is outside the usual course of a mouth ulcer and can rarely be a sign of something more serious. A sore that goes on this long must be checked.

My denture keeps causing sores. I have the same problem again and again. Is there a permanent solution?

Frequently recurring denture sores are a real problem for patients with extensive tooth loss. This is exactly the area we work in for patients who have lost teeth one after another and keep getting sores from a denture; send us your panoramic X-ray and we will write to you within 24 hours about whether a fixed alternative would suit you.

Sources

Send your X-ray and we will tell you which option is realistic for your tooth.

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Next step

Send your X-ray and we will talk through the options.

Share your CBCT or panoramic X-ray. We will write back within 24 hours on which option is realistic for your tooth.

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