Mouth Ulcers: Common Causes and When to Seek Care

Mouth ulcers are small sores that form on the soft tissues inside the mouth and are usually harmless, but they can be painful and affect eating, drinking, and speaking. Most heal on their own, while persistent, severe, or frequently recurring ulcers should be assessed by a dentist or doctor.

Overview

Mouth ulcers, also called oral ulcers, are breaks or sores in the lining of the mouth. They may appear on the inner cheeks, lips, tongue, gums, floor of the mouth, or soft palate. Many people describe them as round or oval sores with a white, yellow, or gray center and a red border.

The most common type is an aphthous ulcer, often known as a canker sore. These ulcers are not the same as cold sores, which are usually caused by the herpes simplex virus and often form on or around the lips. Canker sores are not contagious, although they can be uncomfortable.

In many cases, mouth ulcers are minor and heal without scarring. However, the mouth can also show signs of irritation, infection, immune conditions, vitamin or mineral deficiencies, and, rarely, more serious disease. For this reason, ulcers that do not heal as expected or occur repeatedly should be checked by a qualified dental or medical professional.

Symptoms and What Mouth Ulcers Look Like

Mouth ulcers may cause a stinging, burning, or sharp pain, especially when eating spicy, salty, acidic, or hard foods. Some people notice tingling or tenderness before the ulcer becomes visible. Brushing teeth, speaking, or wearing dentures may also feel uncomfortable while the sore is active.

Typical canker sores are small and shallow. They are usually found inside the mouth rather than on the outer lip. They may occur alone or in small groups, and most heal within 7 to 14 days.

Features that deserve closer attention include ulcers that are unusually large, very painful, spreading, bleeding, hard at the edges, or not healing. Other symptoms such as fever, swollen neck glands, skin rashes, eye irritation, diarrhea, unexplained fatigue, or weight loss can suggest that the ulcer is part of a wider health issue.

Common Causes of Mouth Ulcers

Many mouth ulcers begin after minor injury to the delicate lining of the mouth. Common examples include accidentally biting the cheek, irritation from a sharp tooth edge, hard brushing, dental treatment, orthodontic wires, or ill-fitting dentures. Hot drinks or foods can also burn the oral tissues and lead to a sore area.

Food-related irritation may contribute in some people. Acidic foods such as citrus fruits and tomatoes, spicy foods, salty snacks, or rough-textured foods can trigger or worsen ulcers. Some individuals also react to ingredients in oral care products, including certain foaming agents in toothpaste.

Stress, lack of sleep, and hormonal changes are frequently reported triggers, although the exact mechanism is not always clear. Nutritional deficiencies, particularly low iron, vitamin B12, folate, or zinc, may be linked to recurrent ulcers. Infections such as viral illness, oral thrush, or herpes-related sores can also cause painful lesions in the mouth.

Risk Factors and Related Health Conditions

Some people are more prone to recurrent mouth ulcers because of family tendency, immune system activity, or repeated local irritation. People who wear braces, aligners, retainers, or dentures may have ulcers if an appliance rubs against the mucosa. Dry mouth can also increase irritation because saliva normally helps protect and lubricate oral tissues.

Certain medical conditions can be associated with repeated or persistent oral ulcers. These include celiac disease, inflammatory bowel disease, Behçet disease, oral lichen planus, and some blood or immune disorders. Mouth ulcers may also appear during periods of lowered immunity or after certain infections.

Some medicines can contribute to mouth sores as a side effect, including certain anti-inflammatory medicines, chemotherapy medicines, targeted cancer therapies, and drugs that affect the immune system. A person should not stop prescribed medication without medical advice, but it is important to tell a clinician if mouth ulcers begin after starting a new treatment.

Diagnosis

A dentist or doctor can often diagnose common mouth ulcers by examining the mouth and asking about symptoms, duration, triggers, dental appliances, medicines, diet, and general health. The location and appearance of the sore, whether it recurs, and whether it is accompanied by other symptoms all help guide the assessment.

If ulcers are frequent, severe, or slow to heal, tests may be recommended. These can include blood tests to check for anemia, inflammation, vitamin and mineral deficiencies, or immune-related conditions. If an infection is suspected, a swab or other laboratory test may be used.

When an ulcer persists, has unusual features, or occurs in a person with risk factors for oral disease, the clinician may recommend a biopsy. This means taking a small tissue sample for examination under a microscope. A biopsy is a routine diagnostic step when a sore does not behave like a typical ulcer, and it helps ensure the right treatment plan.

Treatment Options

Treatment depends on the cause, size, severity, and recurrence pattern of the ulcer. Mild canker sores often need only supportive care while they heal. The goal is to reduce pain, protect the sore from irritation, and prevent secondary infection.

Common options may include protective oral pastes, pain-relieving gels, alcohol-free antiseptic mouth rinses, or salt-water rinses. For more painful or recurrent ulcers, a doctor or dentist may prescribe topical corticosteroid preparations, medicated mouthwashes, or other therapies. If a fungal, viral, or bacterial infection is identified, treatment will target that infection.

When ulcers are related to nutritional deficiency, digestive disease, immune conditions, dental trauma, or medications, treating the underlying cause is essential. A sharp tooth may need smoothing, a denture may need adjustment, or a deficiency may need correction under medical guidance. People receiving cancer treatment or immune-suppressing therapy should report mouth sores early so supportive care can be tailored safely.

Prevention and Self-care

Gentle oral care can help ulcers heal and may reduce recurrences. A soft-bristled toothbrush, careful brushing technique, and regular flossing help keep the mouth clean without unnecessary trauma. People who notice irritation from a toothpaste or mouthwash may benefit from discussing alternatives with a dental professional.

During an active ulcer, it is often helpful to avoid spicy, acidic, very hot, salty, or crunchy foods. Softer foods and cool drinks may be more comfortable. Drinking enough water and avoiding tobacco products support the mouth’s natural healing environment.

Helpful self-care steps include:

• Rinsing gently with warm salt water if tolerated.
• Using a protective wax over sharp orthodontic brackets or wires until a dentist can adjust them.
• Avoiding picking, rubbing, or repeatedly touching the sore.
• Keeping a diary of foods, stress, menstrual cycles, medicines, or dental changes that seem to trigger ulcers.
• Scheduling routine dental check-ups to identify sharp teeth, broken fillings, or poorly fitting appliances.

When to See a Doctor or Dentist

Professional care is recommended if a mouth ulcer lasts longer than 2 weeks, keeps coming back, becomes unusually large, or causes significant difficulty eating, drinking, or speaking. A clinician should also assess ulcers that bleed, have hard or raised edges, are associated with a lump in the neck, or appear after starting a new medicine.

People should seek prompt medical advice if mouth ulcers occur with fever, dehydration, severe pain, widespread rash, eye symptoms, genital ulcers, persistent diarrhea, unexplained weight loss, or a weakened immune system. Children, older adults, and people receiving chemotherapy or immune-suppressing medicines may need earlier evaluation.

Most mouth ulcers are treatable and many are preventable once triggers are identified. For international patients who need coordinated dental, oral medicine, dermatology, gastroenterology, or oncology assessment, Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals can diagnose and treat oral ulcer conditions in an integrated setting.

Frequently asked questions

Are mouth ulcers contagious?

Most canker sores, or aphthous ulcers, are not contagious. Cold sores caused by the herpes simplex virus can be contagious and often appear on or around the lips, although they may also affect the mouth. A dentist or doctor can help distinguish between these conditions.

How long do mouth ulcers usually take to heal?

Small, uncomplicated mouth ulcers commonly heal within 7 to 14 days. Larger or deeper ulcers may take longer and can be more painful. Any ulcer that has not healed after 2 weeks should be assessed by a healthcare professional.

Can stress cause mouth ulcers?

Stress does not cause every mouth ulcer, but it can be a trigger for some people, especially when combined with poor sleep, illness, or minor trauma in the mouth. Keeping a symptom diary may help identify a pattern. Stress management, good oral hygiene, and avoiding known food triggers may reduce recurrences.

What foods should be avoided with a mouth ulcer?

Spicy, acidic, salty, crunchy, or very hot foods can sting and delay comfort during healing. Citrus fruits, tomatoes, chips, and heavily seasoned foods are common irritants. Soft, bland foods and cool drinks are often better tolerated until the sore improves.

Do mouth ulcers mean a vitamin deficiency?

Not always. Many ulcers are caused by minor injury, irritation, or individual susceptibility. However, recurrent ulcers can sometimes be linked to low iron, vitamin B12, folate, or zinc, so a doctor may recommend blood tests if ulcers are frequent or severe.

When should a mouth ulcer be checked for oral cancer?

Most mouth ulcers are not cancer, but any sore that does not heal within 2 weeks should be examined. This is especially important if the ulcer has hard edges, bleeds, is painless but persistent, or occurs with a neck lump or unexplained weight loss. Early evaluation helps identify the cause and guide appropriate treatment.

References

• World Health Organization
• American Dental Association
• Mayo Clinic
• National Institute of Dental and Craniofacial Research
• British Dental Association

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.