Mouth Spots and Sores: What They Look Like and When to Worry
Written by NoFrills Dental clinical team
Updated 03/08/2026
Most mouth sores are harmless and heal within one to two weeks. The one rule worth remembering: any ulcer, lump or white or red patch that has not healed after two weeks should be looked at, whether or not it hurts. Painless and persistent is the combination that matters.
- Ordinary mouth ulcers are painful and heal on their own. Most serious lesions do not hurt at all.
- White or red patches that cannot be wiped off need an examination, not a wait.
- Smoking, alcohol and betel quid raise the risk of the patches that matter.
Find your symptom
Sores can appear anywhere on the soft tissues of the mouth: the lips, tongue, gums, inside of the cheeks, floor of the mouth or the palate. This page groups them by what you can actually see, because that is how people search for them, and then explains what each usually means and what to do.
| What you see | Most likely cause |
|---|---|
| Small round painful ulcer with a white or yellow centre | Canker sore (aphthous ulcer) |
| Blister or cluster of blisters on the lip that crusts over | Cold sore (herpes simplex) |
| Creamy white patches that wipe off, leaving a red area | Oral thrush (candidiasis) |
| Firm white patch that does not wipe off | Leukoplakia. Needs assessment. |
| Velvety red patch | Erythroplakia. Needs prompt assessment. |
| Lacy white lines with sore red areas | Lichen planus |
| Cracks and soreness at the corners of the mouth | Angular cheilitis |
| Ulcer or lump that has not healed in two weeks | Needs examination, whatever it looks like |
Painful ulcers and canker sores
Canker sores, or aphthous ulcers, are the most common mouth sore. They are small, round or oval, with a white or yellow centre and a red border, and they hurt out of all proportion to their size. They are not contagious and they usually heal on their own in seven to fourteen days.
Common triggers include a bite or a scratch from a sharp tooth or a hard toothbrush, stress and poor sleep, hormonal changes, sensitivity to sodium lauryl sulphate in some toothpastes, and low levels of iron, folate, vitamin B12 or zinc. Recurrent crops of them can also point to an underlying condition such as coeliac disease or inflammatory bowel disease, which is worth mentioning to a doctor.
Ulcers that keep appearing in the same spot are different: they usually mean something is rubbing there. A sharp filling, a broken tooth, a denture edge or an orthodontic wire can all do it. That is a mechanical problem with a mechanical fix, and it is worth sorting out because chronic irritation is not good for the tissue over years.
White patches and white bumps
The first question with any white patch is whether it wipes off.
If it wipes off and leaves a red, sometimes bleeding surface, it is most often oral thrush, a fungal infection. It is common in denture wearers, in people using inhaled steroids for asthma, after antibiotics, in people with diabetes, and in anyone with a dry mouth. It is treated with antifungal medication, along with fixing the underlying cause, such as cleaning dentures properly and rinsing the mouth after using an inhaler.
If it does not wipe off, it may be leukoplakia: a firm white patch that cannot be scraped away and cannot be explained by anything obvious. Most cases are harmless, but a minority contain precancerous changes, so the standard approach is to examine it, remove the likely cause such as tobacco or a rough tooth edge, and review it. If it does not resolve, a biopsy is the way to be certain. Read more on our page about mouth cancer signs.
Not every white bump is a lesion. Small painless white or yellowish spots on the inside of the cheeks and lips are often Fordyce spots, which are normal oil glands. A soft clear or bluish bubble on the inner lip is usually a mucocele, a blocked minor salivary gland, frequently caused by lip biting. Mucoceles often settle on their own and can be removed if they persist.
Red patches and sore red areas
Erythroplakia is a velvety red patch that cannot be attributed to anything else. It is much less common than leukoplakia and carries a higher chance of precancerous change, so it should be assessed promptly rather than watched.
Oral lichen planus shows up as lacy white lines, often on the inside of the cheeks, sometimes with red, sore or ulcerated areas. It is an immune condition rather than an infection. Mild cases need nothing more than monitoring, and symptomatic cases are treated with topical medication. It is usually kept under review long term.
Denture wearers sometimes develop a red, sore area matching the shape of the denture. That is usually a mix of thrush and pressure, and it is a sign the denture needs adjusting or relining as well as treating.
Sores on the lips and corners of the mouth
Cold sores are caused by the herpes simplex virus. They start with a tingling or burning feeling, then blisters appear on or around the lips, burst and crust over, healing in about seven to ten days. They are contagious while weeping, so avoid kissing and sharing cups or utensils at that stage. Antiviral creams work best applied at the tingling stage, before the blisters appear. Sunlight, illness and stress are common triggers.
Angular cheilitis is soreness, cracking or crusting at one or both corners of the mouth. It is usually a mix of fungal and bacterial infection, often helped along by saliva pooling in the corners. It is common in denture wearers whose bite has collapsed slightly, and can be linked to iron or B vitamin deficiency.
Tongue changes
A sore, smooth, red tongue can point to deficiency of iron, folate or B12 and is worth a blood test. A white coating that brushes off is usually debris and bacteria, and improves with gentle tongue cleaning as part of your daily routine. Map-like patches that move around over weeks are geographic tongue, which is harmless though sometimes sensitive to spicy food.
If the discomfort is really in the jaw joint rather than the soft tissues, see our page on TMJ and jaw pain instead. What does need attention: any ulcer, lump, hard area or white or red patch on the side or underside of the tongue that persists beyond two weeks. Those areas are where mouth cancers most often begin, and early lesions are usually painless.
If something in your mouth has not healed in two weeks, book. It is a ten minute look.
When to see a dentist
Your dentist checks these tissues at every routine check-up, which is how most changes are found early. Book sooner if any of these apply:
- An ulcer, lump or patch that has not healed after two weeks
- A white or red patch that cannot be wiped away
- A sore that is painless but persistent
- Unexplained bleeding, numbness or a lump in the neck
- Difficulty or pain when swallowing, or a persistent hoarse voice
- Ulcers that keep coming back in the same place
- Severe or widespread ulceration, or ulcers with fever and feeling unwell
For context on the timing: cancer referral guidelines in the United Kingdom use three weeks of unexplained ulceration as the threshold for urgent specialist referral. We use two weeks on this page deliberately, because it gives you a margin and because the examination itself is quick and non-invasive. The great majority of people who come in with a persistent sore do not have anything serious.
Source: Cancer Research UK on referral for suspected mouth cancer.
What helps in the meantime
- Rinse with warm salty water a few times a day, or use a mouth rinse your pharmacist recommends
- Avoid spicy, salty, acidic and very crunchy food while it heals
- Switch to a toothpaste without sodium lauryl sulphate if you get frequent ulcers
- Use a soft brush and keep cleaning gently. Plaque around a sore makes it worse
- Topical gels can numb the area or protect it; ask your pharmacist which suits
- If you smoke, drink heavily or chew betel quid, this is the risk factor worth acting on
What not to do: do not put aspirin directly against an ulcer, do not repeatedly test a sore spot with your tongue or fingernail, and do not use strong antiseptic rinses continuously for weeks unless a dentist has told you to.
Something in your mouth that has not healed?
We check the soft tissues of your mouth at every routine visit, and we can look at a specific sore quickly. Find us at Suntec City, Marina Square, Marine Parade and Tanjong Katong.
Frequently asked questions
What causes mouth sores?
Most are caused by minor trauma such as a bite or a sharp tooth edge, viral infections such as herpes simplex, fungal infection such as oral thrush, immune conditions such as lichen planus, or nutritional deficiencies. Less commonly, a persistent sore or patch can be a precancerous change or an early mouth cancer, which is why anything that has not healed in two weeks should be examined.
What does a white patch in my mouth mean?
It depends on whether it wipes off. A creamy white patch that wipes away leaving a red surface is usually oral thrush, a fungal infection that is easily treated. A firm white patch that cannot be wiped off is leukoplakia and should be examined, because a minority of these contain precancerous changes. Small painless white spots on the cheeks or lips are often normal oil glands called Fordyce spots.
How long should a mouth ulcer take to heal?
An ordinary canker sore heals within seven to fourteen days without treatment. If an ulcer is still there after two weeks, is growing, is painless, or keeps returning in exactly the same place, have it looked at rather than waiting longer.
Are mouth ulcers contagious?
Canker sores are not contagious. Cold sores are, because they are caused by the herpes simplex virus, and are most infectious when the blisters are weeping. Oral thrush is not passed on in the ordinary way between healthy adults, though it can be transmitted between a nursing mother and baby.
What is the white bubble on the inside of my lip?
A soft clear or bluish bubble on the inner lip or cheek is usually a mucocele, a minor salivary gland that has been blocked or damaged, often by lip biting. They are harmless and frequently settle on their own. If one keeps coming back or is a nuisance, it can be removed with a simple procedure.
Can a painless sore still be serious?
Yes, and this is the most important point on the page. Early mouth cancers and precancerous patches are usually painless, which is exactly why they get ignored. Pain is a poor guide to seriousness in the mouth. Duration is the better one: two weeks without healing means get it checked.
Related reading
More in this series: bad breath, daily oral hygiene, flossing and interdental cleaning, cavities and tooth decay and TMJ and jaw pain.
Sources: Cancer Research UK on specialist referral for mouth cancer, National Dental Centre Singapore on adult oral health.