Mouth Sores, Ulcers and White Patches: When to See a Dentist
This page is general information and does not replace an examination.
Most mouth sores are ordinary mouth ulcers: they are common, rarely serious and usually heal on their own within a week or two[1]. See a dentist or doctor if an ulcer lasts longer than 3 weeks, or if you notice a red or white patch or a lump in your mouth or on your lip, because these can be early signs of mouth cancer and need to be checked[1][2]. These symptoms are very common and can have other causes, but if cancer is the cause, finding it early may mean it is easier to treat[2]. Our clinic does not take biopsies: when a sore or patch needs further investigation, we refer you to a university faculty of dentistry.
Common types of mouth sores
“Mouth sores” covers several different things: ulcers inside the mouth, blisters on the lips, coatings that wipe off, and patches that do not. Telling them apart helps you decide whether to wait or to have them checked. The table below is a guide, not a diagnosis; a sore that does not fit, or does not heal, needs an examination.
| Type | Typical features | Usual course or next step |
|---|---|---|
| Mouth ulcer (canker sore) | Small white or grey sore with a red border inside the cheeks, lips or on the tongue; not contagious[1][12] | Heals on its own within a week or 2[1] |
| Ulcer from rubbing or biting | Next to a sharp tooth, rough filling, brace or badly fitting denture, or after biting the cheek[1] | Heals once the cause is removed |
| Cold sore | Tingling, itching or burning, then small blisters on or around the lips; contagious[4] | Starts to heal within 10 days[4] |
| Oral thrush | Red mouth with white patches that wipe off and leave red spots; more common with dentures, inhalers or long courses of antibiotics[5] | Antifungal treatment; see a doctor if no better after 1 week of treatment[5] |
| Oral lichen planus | White, lacy pattern inside the cheeks; burning or stinging, especially when eating[1][6] | Can last for years; needs a check[6][8] |
| Leukoplakia (white patch) | White patch that cannot be rubbed away, not usually painful, irregular, sometimes with red areas[7] | Needs a check by a dentist or doctor[7] |
| Red or red-and-white patch | A red patch, or red and white areas together, in the mouth[2][3] | Needs urgent assessment[3] |
Several ulcers at once can also be a sign of hand, foot and mouth disease, oral lichen planus, Crohn’s or coeliac disease, or a weakened immune system; see a doctor if you have ulcers elsewhere on your body or painful, swollen joints.[1]
Most single mouth ulcers have a cause you can try to avoid, such as biting the inside of your cheek, a sharp tooth or rough filling, hot food or drinks, an irritating toothpaste, or being tired or stressed. Others are triggered by things you cannot always control: hormonal changes such as pregnancy, family tendency, a lack of iron, zinc, folic acid, vitamin B or vitamin D, some medicines, or stopping smoking[1].
What helps a mouth ulcer heal
A mouth ulcer needs time; there is no quick fix. Avoiding what irritates it can speed up healing, reduce the pain and lower the chance of it coming back[1]:
- use a soft-bristled toothbrush, drink cool drinks through a straw and eat softer foods[1];
- avoid very spicy, salty or acidic food, rough crunchy food such as toast or crisps, and very hot or acidic drinks such as fruit juice[1];
- avoid toothpaste that contains sodium lauryl sulphate[1];
- rinse with salt water: dissolve half a teaspoon of salt in a glass of warm water, rinse and spit it out[1].
A pharmacist can recommend a product to speed up healing, prevent infection or reduce pain, such as an antimicrobial mouthwash, a painkilling gel, spray or mouthwash, or corticosteroid lozenges; these are available without a prescription[1]. Follow the instructions on the package. For severe, persistent or infected ulcers, a dentist or doctor may prescribe stronger treatment[1].
Cold sores are contagious from the first tingle until they have healed completely: wash your hands after touching one, and do not kiss anyone, especially a baby, while you have one[4]. A pharmacist can recommend antiviral creams and cold sore patches[4].
A dry mouth can make the mouth sore and is covered in our guide to bad breath. Gums that bleed, swell or have a white patch are covered in bleeding gums.
The 3-week rule and other warning signs
Most mouth ulcers are harmless, but a long-lasting ulcer is sometimes a sign of mouth cancer, so it should be checked[1]. NICE, which sets clinical guidance in England, advises considering referral on a suspected cancer pathway for unexplained ulceration in the mouth lasting more than 3 weeks, and urgent assessment by a dentist for a lump on the lip or in the mouth, or a red or red-and-white patch[3].
- a mouth ulcer that has lasted more than 3 weeks[1][2];
- an ulcer that is different from those you have had before, for example bigger than usual or near the back of the throat[1];
- an ulcer that bleeds or becomes more painful and red, which may be a sign of infection[1];
- a red or white patch inside your mouth[2];
- a lump inside your mouth, on your lip, or in your neck or throat[2];
- pain in your mouth that is not going away, difficulty swallowing or speaking, or a hoarse voice that does not go away[2];
- weight loss without trying[2].
These symptoms are very common and are often caused by other conditions; having them does not mean you have cancer. Getting them checked is what matters[2].
White and red patches in the mouth
Not every white patch is a concern. Patches that can be wiped off, leaving red spots, are often oral thrush, which is usually harmless and treated with an antifungal gel[5]. A white patch that cannot be rubbed away may be leukoplakia; it should be checked by a dentist or doctor, who will first rule out other causes such as thrush or cheek biting[7].
Experts convened by the WHO Collaborating Centre for Oral Cancer group several conditions as oral potentially malignant disorders, meaning they carry an increased risk of cancer of the lip or mouth. They include leukoplakia, erythroplakia (red patches), oral lichen planus and oral lichenoid lesions[8]. Increased risk does not mean that most patches become cancer. For leukoplakia, a meta-analysis of 24 studies with 16,604 patients found a pooled malignant transformation proportion of 9.8%, with very wide variation between studies (1.1% to 40.8%); dysplasia in the tissue and the non-homogeneous type were linked with higher risk[9]. The NHS describes this as a small chance of progressing to mouth cancer over time[7].
To find out what a persistent patch is, a biopsy may be needed: a small piece of tissue is removed and examined for abnormal cells[7]. Treatment is not always needed, but regular checks are, and stopping smoking, cutting down on alcohol and not chewing tobacco, paan or betel nut can make a leukoplakia patch smaller or make it go away[7].
Who is more at risk of mouth cancer
Cancers of the lip and oral cavity accounted for an estimated 389,846 new cases and 188,438 deaths worldwide in 2022; they are more common in men and in older people[10]. Tobacco, alcohol and areca nut (betel quid) are among the leading causes, and in North America and Europe human papillomavirus (HPV) infection is responsible for a growing percentage of oral cancers in young people[10].
The NHS lists these factors as making mouth cancer more likely: smoking or chewing tobacco, betel nut or paan; drinking a lot of alcohol; having leukoplakia; a lot of sun or sunbed exposure, which can cause skin cancer of the lips; a previous cancer; and a weakened immune system[11]. You cannot always prevent mouth cancer, but stopping smoking and chewing tobacco, cutting down on alcohol and eating a healthy diet lower the risk[11].
What we do and where we refer
Dr. Ali Cem Ulubey and Dr. Surur Ulubey examine patients themselves; there are no rotating dentists. When you come in with a sore, patch or lump, the dentist examines it and looks for a local cause. This is what happens next:
| Situation | What we do |
|---|---|
| Ulcer next to a sharp or broken tooth edge | Polishing the edge, or a small composite on the broken part, as the case requires |
| Ulcer next to a rough or broken filling | Replacing the filling: composite filling €60, front-tooth aesthetic composite €120 |
| White or red patch, or an ulcer that has not healed in 3 weeks | Referral to a university faculty of dentistry for further investigation; we do not take biopsies in our clinic |
| Lump in the mouth, on the lip or in the neck | Referral to a university faculty of dentistry; a lump in the neck or throat is for a doctor to assess |
| Ulcers with symptoms elsewhere in the body (skin, joints, bowel) | We advise you to see a doctor |
The consultation and the panoramic X-ray taken at the examination have no separate fee. Prices are indicative; your final written quote follows the examination and X-rays and is valid for 30 days. Unless the treatment plan changes, the written price does not change.
If you are not sure whether a sore needs to be seen, you can send a photo on WhatsApp. A photo helps us decide how soon you should be seen; it cannot diagnose a sore or patch and does not replace an examination. Our daily oral care guide covers brushing and toothpaste choice, and oral health and medical conditions explains how illnesses and medicines affect the mouth. Filling types are compared in dental fillings, and how dentures are made and fitted is explained in dentures.
Frequently asked questions
How long does a mouth ulcer last?
Most mouth ulcers heal on their own within a week or two. Avoiding spicy, salty, acidic or rough food, using a soft toothbrush and rinsing with salt water can help. A pharmacist can suggest a mouthwash, gel or lozenge. An ulcer that has not healed after 3 weeks should be checked by a dentist or doctor.
When should I worry about a mouth ulcer?
Have it checked if it lasts more than 3 weeks, is different from ulcers you have had before, bleeds or becomes more painful and red, or comes with a lump, a red or white patch, difficulty swallowing or weight loss. These symptoms often have other causes, but checking early matters: if cancer is the cause, finding it early may make it easier to treat.
Is a white patch in my mouth cancer?
Usually not. White patches that wipe off are often oral thrush, and a white lacy pattern can be lichen planus. A white patch that cannot be rubbed away may be leukoplakia, which carries a small risk of becoming cancer over time. Any white or red patch that does not go away should be examined, and sometimes a biopsy is needed.
What is the difference between a cold sore and a mouth ulcer?
Cold sores usually appear on or around the lips, start with tingling or burning and are contagious until fully healed. Mouth ulcers appear inside the mouth, on the cheeks, lips or tongue, and are not contagious. Cold sores usually heal within 10 days, mouth ulcers within a week or two.
Can a sharp tooth or denture cause mouth ulcers?
Yes. A sharp or broken tooth, a rough filling, braces or a badly fitting denture can rub the inside of the cheek, lip or tongue and cause an ulcer. It usually heals once the cause is fixed, for example by smoothing the tooth or replacing the filling. If it does not heal within 3 weeks, it needs to be checked.
Do you take biopsies at your clinic?
No. We examine the mouth and remove local causes such as a sharp tooth edge or a rough filling. When a sore, white or red patch, or lump needs further investigation, we refer you to a university faculty of dentistry, where a biopsy can be taken if it is needed. We do not offer treatment for the lesion itself.
Sources
- NHS. Mouth ulcers (page last reviewed 11 March 2024; accessed 26 October 2026). www.nhs.uk/conditions/mouth-ulcers
- NHS. Symptoms of mouth cancer (page last reviewed 19 June 2023; accessed 26 October 2026). www.nhs.uk/conditions/mouth-cancer/symptoms
- National Institute for Health and Care Excellence (NICE). Suspected cancer: recognition and referral (NG12), recommendations 1.8.2–1.8.4, oral cancer (accessed 26 October 2026). www.nice.org.uk/guidance/ng12/chapter/Recommendations-organised-by-site-of-cancer
- NHS. Cold sores (accessed 26 October 2026). www.nhs.uk/conditions/cold-sores
- NHS. Oral thrush (mouth thrush) (accessed 26 October 2026). www.nhs.uk/conditions/oral-thrush-mouth-thrush
- NHS. Lichen planus (page last reviewed 2 August 2023; accessed 26 October 2026). www.nhs.uk/conditions/lichen-planus
- NHS. Leukoplakia (page last reviewed 15 May 2024; accessed 26 October 2026). www.nhs.uk/conditions/leukoplakia
- Warnakulasuriya S, Kujan O, Aguirre-Urizar JM, et al. Oral potentially malignant disorders: a consensus report from an international seminar on nomenclature and classification, convened by the WHO Collaborating Centre for Oral Cancer. Oral Dis. 2021;27(8):1862-1880. PMID 33128420. pubmed.ncbi.nlm.nih.gov/33128420
- Aguirre-Urizar JM, Lafuente-Ibáñez de Mendoza I, Warnakulasuriya S. Malignant transformation of oral leukoplakia: systematic review and meta-analysis of the last 5 years. Oral Dis. 2021;27(8):1881-1895. PMID 33606345. pubmed.ncbi.nlm.nih.gov/33606345
- World Health Organization. Oral health: fact sheet (17 March 2025; accessed 26 October 2026). www.who.int/news-room/fact-sheets/detail/oral-health
- NHS. Causes of mouth cancer (page last reviewed 19 June 2023; accessed 26 October 2026). www.nhs.uk/conditions/mouth-cancer/causes
- American Dental Association, MouthHealthy. Canker sores (accessed 26 October 2026). www.mouthhealthy.org/all-topics-a-z/canker-sores
This article is general patient information and does not replace a clinical examination or X-rays.
Editor contact: [email protected] · ulubeydental.com/contact-us
