SymptomMouth & teeth
Mouth Ulcers: What Causes Them and When to Worry
Mouth ulcers are painful, shallow sores on the inside of the cheeks, lips, tongue, gums or palate where the lining has broken down. Most are canker sores (aphthous ulcers) or injuries from biting, braces or sharp teeth, and they heal within 1 to 2 weeks. Viral infections, vitamin and iron deficiencies, celiac disease and Crohn's disease can also cause them. A single ulcer that has not healed after 3 weeks, especially if painless or in a smoker, should be checked for mouth cancer.
Also called: Mouth sores, oral ulcers, canker sores, aphthous ulcers
At a glance
- What they are
- Round or oval sores where the mouth lining has broken, usually white or yellow with a red edge.
- Most common causes
- Canker sores, accidental bites and sharp teeth or braces.
- Other causes
- Cold sores and other viruses, deficiencies (iron, B12, folate), celiac and Crohn's disease, medicines.
- Healing time
- Most heal in 7 to 14 days without scarring.
- When to get checked
- An ulcer lasting over 3 weeks, frequent crops of ulcers, or ulcers with fever or other symptoms.
When to get help
Call 911 or go to the ER
- Mouth sores with blistering or peeling skin elsewhere, red eyes and fever, especially after starting a new medicine (possible Stevens-Johnson syndrome)
- Mouth sores with difficulty swallowing saliva, drooling or difficulty breathing
See a doctor within a day or two
- A child with mouth sores who is refusing to drink or has signs of dehydration, such as few wet diapers
- Many painful sores on the gums and mouth with high fever (possible first herpes infection)
- Mouth ulcers with a very low white cell count, during chemotherapy or with a weakened immune system
Book a routine appointment
- A single ulcer or red or white patch that has not healed within 3 weeks
- A painless ulcer, lump or thickened area, especially if you smoke or drink alcohol heavily
- Ulcers that come back frequently or are larger than 1 cm (half an inch)
- Mouth ulcers with genital ulcers, diarrhea, weight loss, joint pain or red eyes
Usually safe to manage at home
- One or a few small, painful ulcers that started after a bite, a sharp tooth or stress, and are improving within a week
What a mouth ulcer looks like
A typical ulcer is round or oval, with a white, gray or yellow base and a red, inflamed border. It stings with spicy, salty or acidic food. Ulcers form on the soft, moving parts of the mouth: inside the lips and cheeks, under or on the sides of the tongue, and the floor of the mouth.
Causes of mouth ulcers
Canker sores (aphthous ulcers)
The most common cause of recurring ulcers. They are not contagious. Triggers include minor injury, stress, hormonal changes around periods, certain foods, toothpastes containing sodium lauryl sulfate, and stopping smoking. They often start in childhood or the teens and run in families. The condition page on mouth ulcers explains types and treatment of recurrent canker sores in detail.
Injury
- biting your cheek or tongue
- sharp or broken teeth, rough fillings, dentures or braces
- hot food and drink burns
- harsh brushing
These usually heal within a week or two once the cause is removed.
Infections
- Oral herpes: the first infection, usually in young children, causes many painful ulcers on the gums and mouth with fever (gingivostomatitis). Later outbreaks appear as cold sores on the lip.
- Hand, foot and mouth disease and herpangina: common in children, with sores at the back of the mouth, fever and sometimes spots on the hands and feet.
- Others: syphilis, HIV, tuberculosis and fungal infections are rare causes.
Deficiencies and medical conditions
- Iron, vitamin B12 and folate deficiency. See vitamin B12 deficiency.
- Celiac disease and Crohn's disease.
- Behçet's disease: recurrent mouth and genital ulcers with eye and skin inflammation.
- Lupus, reactive arthritis and periodic fever syndromes in children.
- Oral lichen planus: white lacy patches with painful sore areas.
Medicines
NSAIDs, nicorandil, beta blockers, methotrexate, chemotherapy and some other medicines can cause ulcers.
Mouth cancer
Oral cancer can begin as an ulcer that does not heal, a red or white patch, or a lump, often painless at first. The main risk factors are smoking, chewing tobacco or betel nut, heavy alcohol use and HPV infection. See oral cancer.
Telling mouth ulcers apart
| Feature | Canker sore | Herpes | Injury | Possible cancer |
|---|---|---|---|---|
| Where | Inside cheeks, lips, tongue | Gums, palate (first infection); lip edge (cold sore) | Where teeth or appliances rub | Sides of tongue, floor of mouth |
| Looks like | Round, white with red rim | Clusters of tiny blisters that merge | Irregular, matches the source | Ragged, hard edges, or a red or white patch |
| Pain | Painful | Painful, often with fever | Painful | Often painless at first |
| Heals | 1 to 2 weeks | 1 to 2 weeks | Within 2 weeks of removing the cause | Does not heal |
How doctors find the cause
A doctor or dentist examines the mouth and asks how often ulcers occur, how long they last and about other symptoms. Blood tests for blood count, iron, B12, folate and celiac antibodies are common for recurrent ulcers. An ulcer lasting more than 3 weeks usually needs a biopsy.
Treatment and home care
- Rinse with warm salt water or an antiseptic mouthwash.
- Protect the ulcer: pharmacy gels, pastes or protective films that coat the ulcer.
- Numb the pain: benzocaine or lidocaine gels, following the label. Do not use benzocaine products in children under 2.
- Avoid triggers: spicy, salty, acidic and crunchy foods; try an SLS-free toothpaste.
- Brush gently with a soft toothbrush.
- Pain relief: acetaminophen (paracetamol) or ibuprofen, following the label dose.
- For children, keep them drinking: cold drinks, ice pops and soft foods help.
See a dentist about sharp teeth or poorly fitting dentures or braces.
Frequently asked questions
What causes mouth ulcers?
Most are canker sores triggered by minor injury, stress, hormonal changes or certain foods, or are caused directly by bites, sharp teeth or braces. Viral infections, low iron, B12 or folate, celiac disease, Crohn's disease and some medicines are less common causes.
When should I worry about a mouth ulcer?
See a dentist or doctor if an ulcer has not healed within 3 weeks, is painless, is getting bigger, or you smoke or drink heavily. Also get checked for frequent or very large ulcers, or ulcers with fever, weight loss, diarrhea, genital sores or joint pain.
Are mouth ulcers contagious?
Canker sores and injury ulcers are not contagious. Ulcers caused by viruses, such as herpes and hand, foot and mouth disease, are contagious through saliva and close contact. Avoid kissing and sharing cups while sores are present.
How long do mouth ulcers last?
Most canker sores and injury ulcers heal within 7 to 14 days. Larger "major" aphthous ulcers can take several weeks and may scar. An ulcer lasting more than 3 weeks should be examined.
Why do I keep getting mouth ulcers on my tongue?
Recurring tongue ulcers are often canker sores or from biting or a sharp tooth. Frequent ulcers can also signal low iron, B12 or folate, or celiac disease, which a blood test can check. A persistent ulcer on the side of the tongue needs examination.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Oral Medicine: Aphthous ulcers
- NHS: Mouth ulcers
- MedlinePlus: Canker sore; Mouth ulcers
- American Dental Association (MouthHealthy): Canker sores
- NICE Clinical Knowledge Summaries: Aphthous ulcer