Mouth Ulcers: Causes, Symptoms, Treatment and When to Seek Care

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Quick Answer: What is a mouth ulcer?

A mouth ulcer is a painful sore inside the mouth that can affect the gums, tongue, palate, inner cheeks or lips. Canker sores are the most common type. Mouth ulcers are not contagious, unlike cold sores, which usually appear on the lips. Most last about 10 to 14 days, and a sore lasting longer than three weeks needs assessment.

Mouth ulcers can occur in several areas inside the mouth. Illustration for Rinnit.com; not a diagnostic image.

What the research says

• Lower vitamin B12 and hemoglobin levels are linked with recurrent canker sores. A systematic review and meta-analysis found that people with recurrent aphthous stomatitis (recurring canker sores) had lower vitamin B12 and hemoglobin than healthy controls (standardized mean difference −0.52, 95% CI −0.89 to −0.14, and −0.58, 95% CI −0.90 to −0.27). They also had higher odds of vitamin B12 deficiency (OR 2.93, 95% CI 2.28–3.78), ferritin deficiency (OR 2.50, 95% CI 1.48–4.22) and reduced hemoglobin (OR 2.14, 95% CI 1.38–3.32). Results for folic acid, iron and zinc were not statistically significant. These are associations, not proof that a deficiency caused any one ulcer (Mousavi et al., BMC Oral Health, 2024). [2]

• Most white mouth patches (leukoplakia) do not become cancer, but some features raise the risk. Across 55 studies including 41,231 people with oral leukoplakia, the pooled malignant transformation proportion was 6.64% (95% CI 5.21–8.21%). Risk was higher for non-homogeneous lesions (RR 4.23, 95% CI 3.31–5.39) and lesions with epithelial dysplasia (RR 2.75, 95% CI 2.26–3.35) (Pimenta-Barros et al., Oral Dis, 2025). [3]

• Red patches (erythroplakia) carry a much higher transformation rate than white patches. In a meta-analysis of 92 studies, the pooled malignant transformation rate was 33.1% for erythroplakia (99% CI 13.6–56.1%), 9.5% for leukoplakia (99% CI 5.9–14.0%) and 1.4% for lichen planus (99% CI 0.9–1.9%). The wide interval for erythroplakia reflects limited data, and these figures describe groups, not any one person’s risk (Iocca et al., Head Neck, 2020). [4]

What do mouth ulcers look and feel like?

Mouth ulcers are usually visible sores. They are commonly red around the edges with a white, yellow or gray center, and there may be one sore or more than one. Swelling around the ulcer can occur. [1]

Feature	What a person may notice
Location	A sore on the gums, tongue, roof of the mouth, inner cheek or inner lip.
Color	Red around the edges with a white, yellow or gray center.
Number	One ulcer or several ulcers.
Sensation	Pain, tenderness or swelling around the sore.
Daily impact	More soreness while brushing, or pain that worsens with spicy, salty or sour foods.

Pain can make ordinary activities uncomfortable, including eating, drinking and speaking. Symptoms alone cannot identify the exact type or cause of a mouth sore.

What are the common types of mouth sores?

Several different conditions can produce sores or patches inside the mouth. The following table summarizes common patterns; it is not a tool for diagnosing an individual sore.

Type or pattern	Description
Canker sores, also called aphthous ulcers	The most common type of mouth ulcer; often white or yellow with red edges. The cause is frequently unclear, although minor trauma, acidic foods and stress may contribute.
Oral lichen planus	May cause itchy rashes and lacelike white sores inside the mouth and reflects an immune-system response.
Leukoplakia	Causes white or gray patches; chronic irritation such as smoking or chewing tobacco can contribute, although it may also occur without an apparent reason. These lesions usually are not cancerous.
Erythroplakia	Causes red patches, commonly behind the lower front teeth or under the tongue. These patches are usually precancerous or cancerous and need healthcare evaluation.
Oral thrush	A fungal infection that can cause red and creamy-white sores or patches; it can occur after antibiotic treatment or when the immune system is weaker than usual.
Mouth-cancer lesions	May appear as red or white sores or ulcers and do not heal on their own. A mouth ulcer that lasts beyond three weeks should be reported to a healthcare provider.

The word “ulcer” describes the appearance of a sore, not necessarily a single disease. Because several conditions can look similar, persistent, unusual or painless sores deserve professional assessment.

Common locations and follow-up cues for mouth ulcers. Illustration for Rinnit.com; not a diagnostic chart.

What causes mouth ulcers?

Mouth ulcers can follow local irritation or injury, changes in the body, or an associated health condition. Common contributors include tissue injury during dental work, accidentally biting the cheek or tongue, braces or retainers, harsh or abrasive toothpaste, acidic foods, hormonal changes during a period, stress and lack of sleep. [1]

Some mouth ulcers are associated with vitamin deficiencies; viral, bacterial or fungal infections; and conditions such as Crohn’s disease, celiac disease, reactive arthritis, lupus and Behçet’s disease. An associated condition is not confirmed simply because an ulcer is present. [1]

Possible contributor	Example
Local injury or irritation	Dental work, biting the cheek or tongue, braces or retainers, or abrasive toothpaste.
Food-related irritation	Eating many acidic foods; pain may also worsen with spicy, salty or sour foods.
Body changes	Hormonal changes during a period.
Lifestyle or emotional factors	Stress and lack of sleep.
Associated health conditions	Vitamin deficiencies, infections, some autoimmune conditions and some gastrointestinal conditions.

If sores recur frequently or appear alongside other symptoms, a clinician can help decide whether further evaluation is appropriate.

Are mouth ulcers contagious?

No. Mouth ulcers are not contagious and do not spread through kissing or sharing food. This differs from cold sores, which usually appear outside the mouth, often on the lips, are caused by a virus and are contagious. [1]

A sore on or around the mouth should not be classified by location alone. If you are unsure whether a lesion is a mouth ulcer or a cold sore, ask a healthcare provider or dentist for an assessment.

How are mouth ulcers diagnosed?

A healthcare provider can often diagnose a mouth ulcer with a visual examination. If there is a severe breakout or concern about a specific health condition, the provider may order blood tests. [1]

For a visit, note when the sore started, whether new sores appear before older ones heal, where the sore is located, whether it is painful, what makes it worse and whether fever or diarrhea is also present. This organizes the history you share; it does not replace a clinical examination.

How are mouth ulcers treated, and what relieves symptoms?

Most mouth sores heal on their own, but a healthcare provider may prescribe treatment to ease discomfort. Options include antiseptic gels or mouth rinses, steroid ointments and, for severe cases, immunosuppressants. The choice depends on the clinical situation and should be discussed with a qualified healthcare provider. [1]

Supportive steps that may relieve symptoms while a sore heals include drinking plenty of water, keeping the mouth clean with good oral hygiene, rinsing with warm saltwater a few times each day, avoiding hot and spicy foods until the ulcer heals, and considering an over-the-counter topical anesthetic. [1]

One home option mentioned in clinical guidance is a rinse made from equal parts hydrogen peroxide and water twice daily. Because a mouth rinse or topical product may not be appropriate for everyone, confirm how to use any product with a healthcare professional or follow its directions carefully. Do not use this article to select a product, treatment course or dose. [1]

Goal	Options to discuss or consider
Keep comfortable and hydrated	Drink plenty of water.
Reduce irritation	Avoid hot and spicy foods while the ulcer heals.
Keep the mouth clean	Continue good oral hygiene.
Soothe symptoms	Warm saltwater rinses or an appropriate topical anesthetic may help.
Treat a more serious or persistent problem	Arrange professional evaluation; prescribed treatment may be needed.

A practical, non-diagnostic symptom-relief and follow-up pathway. Illustration for Rinnit.com.

How long do mouth ulcers last?

In most cases, mouth ulcers go away on their own in about 10 to 14 days. A mouth sore that lasts longer than three weeks should be assessed by a healthcare provider. [1]

A sore that does not heal is not automatically cancer, but persistent mouth sores can point to an underlying health condition and should not be ignored.

Can mouth ulcers be prevented?

Mouth ulcers cannot be prevented altogether, but several steps may reduce risk: brushing twice daily, flossing once daily, using a soft-bristled toothbrush, eating a healthy diet rich in fresh fruits and vegetables, and attending regular dental checkups and cleanings. [1]

If a healthcare provider believes an underlying condition is contributing to recurring sores, managing that condition may reduce the risk of ulcers returning.

Prevention habit	Why it matters
Brush twice daily	Supports oral health.
Floss once daily	Supports oral hygiene between teeth.
Use a soft-bristled toothbrush	Helps avoid tissue irritation.
Eat a healthy diet with fresh fruits and vegetables	Supports a healthy dietary pattern.
Keep regular dental checkups and cleanings	Creates opportunities for oral assessment and cleaning.
Discuss recurring sores	An underlying condition may need management.

When should you seek medical or dental care for a mouth ulcer?

Arrange a healthcare appointment for a mouth sore that lasts three weeks or longer. You should also seek guidance for new sores that appear before older ones heal, ulcers affecting the outer part of the lips, pain that does not improve with medication, unusually large ulcers, painless mouth sores, fever or diarrhea. [1]

A sore that will not heal deserves particular attention because some persistent mouth lesions can be associated with conditions that need treatment. This article cannot determine whether a specific sore is harmless.

Questions to bring to an appointment

If mouth ulcers are severe or frequent, consider asking:

• Why do I keep getting these sores?

• Could an underlying condition be contributing?

• How can I reduce my risk?

• What treatment is appropriate?

• Are there changes to my diet or lifestyle that may help?

How is a mouth ulcer different from a canker sore or cold sore?

“Mouth ulcer” is the broad term for a sore or ulceration inside the mouth. A canker sore is the most common type of mouth ulcer, and many people use the terms interchangeably. Canker sores can recur over a person’s lifetime and often have no known cause, although deficiencies and triggers may be involved in some cases. [1]

A cold sore is different: it usually forms outside the mouth, often on the lips, is caused by a virus and is contagious. Canker sores are inside the mouth and are not contagious. [1]

Feature	Mouth ulcer / canker sore	Cold sore
Usual location	Inside the mouth, including gums, tongue, palate, inner cheeks or inner lips.	Outside the mouth, often on the lips.
Contagious?	No.	Yes.
Relationship	“Mouth ulcer” is a broad term; canker sores are the most common type.	A different, virus-caused lesion.

Conclusion

Most mouth ulcers are uncomfortable but temporary. They often improve in about 10 to 14 days, and basic oral care, hydration and avoiding irritating foods may make the healing period easier.

The most important checkpoint is duration and pattern. If a sore lasts three weeks or longer, keeps recurring before earlier sores heal, is unusually large or painless, affects the outer lips, or occurs with fever or diarrhea, arrange professional care. For more clear health explainers, explore Rinnit.com’s health library and bring questions about recurring or unusual mouth sores to a qualified clinician or dentist.

Frequently Asked Questions

Are mouth ulcers contagious?

No. Mouth ulcers are not contagious and do not spread through kissing or sharing food. Cold sores are different: they usually appear outside the mouth, are caused by a virus and are contagious.

What is the fastest way to heal a mouth ulcer?

Most mouth ulcers heal on their own in about 10 to 14 days. Hydration, good oral hygiene, warm saltwater rinses, avoiding hot and spicy foods, and some topical products are ways to relieve symptoms; a healthcare provider may prescribe treatment when needed.

Can stress cause mouth ulcers?

Stress is one of several listed contributors, along with lack of sleep, minor injury, acidic foods, hormonal changes and other factors. Stress alone does not prove why a particular sore appeared.

Can a mouth ulcer be a sign of cancer?

Usually not, but a persistent sore can be associated with conditions that need evaluation, including oral cancer. A sore that does not heal or lasts longer than three weeks should be discussed with a healthcare provider.

What foods can make a mouth ulcer hurt more?

Pain may worsen with spicy, salty or sour foods. Acidic foods are also listed as a possible contributor for some ulcers, and avoiding hot and spicy foods until the ulcer heals is recommended.

Should I keep brushing my teeth with a mouth ulcer?

Maintaining good oral hygiene and using a soft-bristled toothbrush is recommended. Brushing may feel more sore around an ulcer, so discuss persistent pain or difficulty cleaning with a dental or healthcare professional.

When should I see a dentist or healthcare provider?

Seek professional guidance for a sore lasting three weeks or longer, new sores before old ones heal, ulcers on the outer lips, pain not improving with medication, unusually large or painless sores, fever or diarrhea.

References

1. Cleveland Clinic. Mouth Ulcers: Types, Causes & Treatment. Cleveland Clinic. Last updated June 6, 2023. https://my.clevelandclinic.org/health/diseases/21766-mouth-ulcer

2. Mousavi T, Jalali H, Moosazadeh M. Hematological parameters in patients with recurrent aphthous stomatitis: a systematic review and meta-analysis. BMC Oral Health. 2024;24(1):339. PMID 38493289. https://doi.org/10.1186/s12903-024-04072-5

3. Pimenta-Barros LA, Ramos-García P, González-Moles MÁ, et al. Malignant transformation of oral leukoplakia: systematic review and comprehensive meta-analysis. Oral Dis. 2025;31(1):69-80. PMID 39314164. https://doi.org/10.1111/odi.15140

4. Iocca O, Sollecito TP, Alawi F, et al. Potentially malignant disorders of the oral cavity and oral dysplasia: a systematic review and meta-analysis of malignant transformation rate by subtype. Head Neck. 2020;42(3):539-555. PMID 31803979. https://doi.org/10.1002/hed.26006

Disclaimer

This article is for general educational purposes and is not a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified healthcare professional with any questions about a medical condition or treatment.