Mouth Ulcers: How to Tell a Common Ulcer From One That Needs Checking
Mouth ulcers are small, sore spots inside the mouth, and almost everyone gets one at some point. Most are harmless and heal on their own. A few are not, which is why it helps to know what a common ulcer looks like and when one should be looked at.
This guide covers what causes mouth ulcers, how a typical ulcer differs from one that needs checking, how long they usually last, what may ease the discomfort and what happens at a check-up. It stays with ulcers, so it doesn’t cover other mouth problems.
This article is general information only. It is not a diagnosis. If you are unsure about an ulcer, have it checked.
What are Mouth Ulcers?
A mouth ulcer is a break or sore patch in the soft lining of the mouth. It can affect the tongue, the lining of the cheeks and lips, or the soft tissues beneath the tongue and across the roof of the mouth.
Most are the common, short-lived kind that dentists call aphthous ulcers or canker sores. Others form where the lining has been damaged or irritated. Cold sores are a different condition, and they usually appear on or around the lips.
What Causes Mouth Ulcers?
Often, no clear cause is found. The causes a dentist can most often spot are local ones, inside the mouth:
- Biting your cheek, lip or tongue, or brushing too hard.
- Hot food or drink that burns the lining.
- A sharp or broken tooth, or a rough edge on a filling or crown.
- A denture, retainer or other appliance that rubs.
- Sensitivity to an ingredient in an oral care product.
Other triggers, such as stress, hormonal changes or general health, can also play a part. If you get ulcers often with no local cause, your doctor can help look into these.
Common Ulcer or One to Get Checked? A Side-by-Side Guide
This is a general guide only. Only an examination can tell you which applies.
| A typical ulcer | Worth getting checked | |
| Look | Round or oval, with a pale centre and a red edge | Irregular edges, raised or hard, or a red or white patch around it |
| Feel | Tender or stinging, especially with food | Often painless, or a lump or thickening nearby |
| Healing | Improves steadily, usually within about one to two weeks | Not healed within two weeks |
| Pattern | One ulcer, or a few that clear | Keeps coming back in the same place, or several that don’t clear |
| Other signs | None | Bleeding with no cause, numbness, trouble swallowing or moving the tongue, fever or feeling unwell |
Pain is not a reliable guide. A painless ulcer that does not heal needs checking just as much as a painful one.
How Long do Mouth Ulcers Last?
Victoria’s Better Health Channel advises that most mouth ulcers are harmless and heal by themselves in about 10 to 14 days (Better Health Channel, “Mouth ulcers”, reviewed 13 October 2025). Larger ulcers can take longer.
Healing time varies between patients. What matters is whether an ulcer is clearly improving or has stalled.
How to Get Rid of Mouth Ulcers: What Helps and What to Avoid
There is no quick fix for mouth ulcers, and most heal on their own. Some steps may make you more comfortable while you wait:
- Avoid irritants. Skip hot, spicy, salty, acidic and crunchy foods until it settles.
- Choose soft, bland foods and lukewarm or cool drinks.
- Rinse gently with lukewarm salty water.
- Keep your mouth clean, brushing gently with a soft toothbrush and keeping the brush away from the sore spot where you can.
- Don’t pick at it. This can slow healing.
- Ask a pharmacist or your dentist about products made for mouth ulcers, and follow the label.
Home care can ease discomfort, but it does not treat the cause, and results vary. It is not a substitute for a check if an ulcer lingers.
Ulcers That Keep Appearing In the Same Spot
If an ulcer returns in the same place, something nearby may be irritating the lining. Common causes are a sharp tooth edge, a rough filling or crown, a denture or retainer that rubs, or a habit of biting the cheek.
This is something a dentist can often find and fix, for example by smoothing a rough edge or adjusting an appliance. It won’t always be the cause, but it is worth checking before you assume it is just bad luck. Please don’t try to file or adjust a tooth or appliance yourself.
When to See a Dentist About a Mouth Ulcer
Most ulcers are nothing to worry about. If anything in the right-hand column of the table applies to you, book a check, especially if an ulcer has not healed within two weeks.
An ulcer that does not heal is one of the signs dentists look for when screening for mouth cancer. Most ulcers that last a bit longer turn out to be harmless, but a persistent one is worth having looked at early.
If you have a fever or feel generally unwell, see your doctor. If swelling affects your breathing or swallowing, call 000 or go to your nearest hospital emergency department. Our page on soft tissue injuries in the mouth covers cuts and knocks inside the mouth.
What Happens At a Mouth Ulcer Check-Up
At an examination, your dentist can:
- Ask when the ulcer appeared, how long it has been there and whether you have had others.
- Look at and feel the ulcer and the tissue around it.
- Check the rest of your mouth and the glands in your neck.
- Look for causes such as sharp teeth, rough dental work or a denture that rubs.
- Smooth or adjust an irritant where possible.
- Advise on managing the discomfort.
- Suggest further assessment, or seeing your doctor, if an ulcer is persistent or unusual.
Our general dentistry page gives an overview of care at Epsom Dental Care. If you also have persistent bad breath, our article on what causes bad breath explains the common causes.
Mouth Ulcers FAQs
Is a painless ulcer less serious?
Not necessarily. Pain is not a reliable guide to how serious an ulcer is. A painless ulcer that has not healed within two weeks should be checked.
Can my dentures, braces or retainer cause ulcers?
Yes, if they rub on the lining. Tell your dentist rather than adjusting them yourself, as they can check the fit and smooth any rough spots.
Can I use mouthwash on an ulcer?
Some rinses sting an open sore. Ask your pharmacist or dentist what suits you before using a product on an ulcer, and follow the label.
Can a photo tell me what my ulcer is?
Photos can’t reliably show what an ulcer is or why it has formed. If you are unsure, have it examined.
Book a Mouth Ulcer Check-Up in Belmont WA
Got an ulcer that has not healed in two weeks, or ulcers that keep coming back? The next step is an examination.
At Epsom Dental Care, your dentist can look at your mouth, check for causes such as sharp teeth or rubbing dental work, explain what they find and advise whether further assessment is needed. You can also read about our dental check-ups.
Call us on (08) 9478 2349 or request an appointment online to arrange a mouth ulcer check-up.
We are at 5/132 Epsom Ave, Belmont WA 6104, and we welcome patients from Belmont, Redcliffe, Ascot, Kewdale and Rivervale.
Source: Better Health Channel, Victorian Department of Health, “Mouth ulcers”, reviewed 13 October 2025.
This article is general information and does not replace advice from a registered dental practitioner or doctor. Results vary between patients. Ask your dentist whether treatment is appropriate for you.