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Mouth Sores and Inflammation



Bernard J. Hennessy

, DDS, Texas A&M University, College of Dentistry

Last full review/revision Jun 2020| Content last modified Jun 2020

Mouth sores and inflammation vary in appearance and size and can affect any part of the mouth, including the lips (see Lip Sores and Inflammation).

People may have swelling and redness of the lining of the mouth or individual, painful ulcers. An ulcer is a sore that forms a hole in the lining of the mouth when the top layer of cells breaks down. Many ulcers appear red, but some are white because of dead cells and food debris inside the center portion. Blisters are sores that are raised and filled with clear fluid (they are called vesicles or bullae, depending on size). Rarely, the mouth looks normal even though people have symptoms of mouth inflammation (burning mouth syndrome).

Noncancerous (benign) ulcers are usually painful until healing is well under way. The pain makes eating difficult, which sometimes leads to dehydration and undernutrition. Some sores go away but recur.

Causes of Mouth Sores and Inflammation

There are many types and causes of mouth sores. Mouth sores may be caused by an infection, a bodywide (systemic) disease, a physical or chemical irritant, or an allergic reaction (see table Some Causes of Mouth Sores). Often the cause is unknown. In general, because the normal flow of saliva helps protect the lining of the mouth, any condition that decreases saliva production makes mouth sores more likely (see Dry Mouth).

The most common specific causes of mouth sores are

  • Recurrent aphthous stomatitis (canker sores)
  • Viral infections (particularly herpes simplex and herpes zoster)
  • Other infections (caused by fungi or bacteria)
  • Injury or irritating food or chemicals
  • Tobacco use
  • Drugs (particularly chemotherapy drugs) and radiation therapy
  • Systemic disorders

Viral infections

Viruses are the most common infectious causes of mouth sores. Cold sores of the lip and, less commonly, ulcers on the palate caused by the herpes simplex virus are perhaps the most well known. However, many other viruses can cause mouth sores. Varicella-zoster, the virus responsible for chickenpox as well as the painful skin disorder called shingles, can cause multiple sores to form on one side of the mouth. These sores are the result of a flare-up of the virus, which, just like herpes simplex virus, never leaves the body. Occasionally, the mouth remains painful for months or years or even permanently after the sores have healed.

Other infections

A bacterial infection can lead to sores and swelling in the mouth. Infections may be caused by an overgrowth of organisms normally present in the mouth or by newly introduced organisms, such as the bacteria that cause syphilis or gonorrhea. Bacterial infections from teeth or gums can spread to form a pus-filled pocket of infection (abscess) or cause widespread inflammation (cellulitis).

Syphilis may produce a red, painless sore (chancre) that develops in the mouth or on the lips during the early stage of infection. The sore usually heals after several weeks. About 4 to 10 weeks later, a white area (mucous patch) may form on the lip or inside the mouth if the syphilis has not been treated. Both the chancre and the mucous patch are highly contagious, and kissing may spread the disease during these stages. In late-stage syphilis, a hole (gumma) may appear in the palate or tongue. The disease is not contagious at this stage.

The yeast Candida albicans is a normal resident of the mouth. However, it can overgrow in people who have taken antibiotics or corticosteroids or who have a weak immune system, such as people with AIDS. Candida can cause whitish, cheese-like patches that destroy the top layer of the lining of the mouth (thrush) when wiped off. Sometimes only flat, red areas appear.

Injury or irritation

Any type of damage or injury to the mouth, for instance, when the inside of the cheek is accidentally bitten or scraped by broken or jagged teeth or poor-fitting dentures, can cause blisters (vesicles or bullae) or ulcers to form in the mouth. Typically, the surface of a blister breaks down quickly (ruptures), forming an ulcer.

Many foods and chemicals can be irritating or trigger a type of allergic reaction, causing mouth sores. Acidic foods, cinnamon flavoring, or astringents may be particularly irritating, as can certain ingredients in common substances such as toothpaste, mouthwash, candy, and gum.


Tobacco use can cause mouth sores. The sores most likely result from exposure to the irritants, toxins, and carcinogens found naturally in tobacco products but may also result from the drying effects on the lining of the mouth, the high temperatures in the mouth, changes to the acidity of the mouth, or decreased resistance to viral, bacterial, and fungal infections.

Drugs and radiation therapy

The most common drugs causing mouth sores include certain cancer chemotherapy drugs. Drugs containing gold, which were once used to treat rheumatoid arthritis and some other autoimmune disorders, can also cause mouth sores, but these drugs are rarely used because safer and more effective drugs are now available. Radiation therapy is also a common cause of mouth sores. Rarely, people may develop mouth sores after taking antibiotics.

Systemic disorders

Many diseases affect the mouth along with other parts of the body. Behçet disease, an inflammatory disease affecting many organs, including the eyes, genitals, skin, joints, blood vessels, brain, and gastrointestinal tract, can cause recurring, painful mouth sores. Stevens-Johnson syndrome, a type of allergic reaction, causes skin blisters and mouth sores. Some people with inflammatory bowel disease also develop mouth sores. People with severe celiac disease, which is caused by an intolerance to gluten (a component of wheat and some other grains), often develop mouth sores. Lichen planus, a skin disease, can rarely cause mouth sores, although usually these sores are not as uncomfortable as those on the skin. Pemphigus vulgaris and bullous pemphigoid, both skin diseases, can also cause blisters to form in the mouth.

Nutritional deficiencies of iron, vitamin B, and vitamin C may also cause mouth sores.

Evaluation of Mouth Sores and Inflammation

Not all mouth sores require immediate evaluation by a doctor. The following information can help people decide whether a doctor’s evaluation is needed and help them know what to expect during the evaluation.

Warning signs

In people with mouth sores, certain symptoms and characteristics are cause for concern for systemic disorders. They include

  • Fever
  • Blisters on the skin
  • Inflammation of the eye
  • Any sores in people with a weakened immune system (such as people with HIV infection)

When to see a doctor

People who have warning signs should see a doctor right away. People who have no warning signs but have a lot of pain, feel generally ill, and/or have trouble eating should see a doctor within several days. All people with a sore that lasts for 10 days or more must be examined by a dentist or doctor to ensure that the sore is not cancerous or precancerous.

What the doctor does

Doctors first ask questions about the person's symptoms and medical history. Doctors ask people about their consumption of or exposure to food, drugs, and other substances (such as tobacco, chemicals, toothpaste, mouthwashes, metals, fumes, or dust). Doctors need to know about all currently known conditions that might cause mouth sores (such as herpes simplex, Behçet disease, or inflammatory bowel disease), conditions that are risk factors for mouth sores (such as a weakened immune system, cancer, or HIV infection), and the person’s sexual history.

Doctors then do a physical examination. The mouth is inspected, noting the location and nature of any sores. Doctors then do a general examination to look for signs of systemic disorders that could affect the mouth. The skin, eyes, and genitals are examined for any sores, blisters, or rashes.

What doctors find during the history and physical examination often suggests a cause of the mouth sores and the tests that may need to be done.

Some Causes of Mouth Sores



Bacterial infections



Trench mouth (acute necrotizing ulcerative gingivitis)

Fungal infections

Candidal infections (most common)

Viral infections

Chickenpox (varicella zoster)

Herpes simplex infection (primary or secondary)

Shingles (reactivation of varicella zoster)

Others (such as infection by coxsackievirus, cytomegalovirus, Epstein-Barr virus, or HIV, as well as genital warts, influenza, and measles)

Systemic disorders

Behçet disease

Bullous pemphigoid or pemphigus vulgaris

Celiac disease

Cyclic neutropenia

Erythema multiforme

Inflammatory bowel disease

Iron deficiency

Kawasaki disease


Platelet disorders

Stevens-Johnson syndrome

Thrombotic thrombocytopenia

Vitamin B deficiency (pellagra)

Vitamin C deficiency (scurvy)



Antiseizure drugs*


Chemotherapy drugs



Nonsteroidal anti-inflammatory drugs (NSAIDs)*

Physical irritation

Cheek-biting or lip-biting habits

Dentures that fit poorly

Jagged or broken teeth

Irritants and allergies

Acidic foods

Allergic reaction to ingredients in toothpaste, mouthwash, candy, gum, dyes, or lipstick

Aspirin, when applied to tissues inside the mouth

Dental appliances containing nickel or palladium

Occupational exposure to dyes, heavy metals, acid fumes, or metal or mineral dust

Tobacco (chewing and/or smoking)


Burning mouth syndrome

Canker sores (recurrent aphthous stomatitis)

Lichen planus

Radiation therapy to the head and neck

* Rare causes of mouth sores.


  • Sometimes cultures, blood tests, or biopsy

The need for tests depends on what doctors find during the history and physical examination, particularly whether warning signs are present. People with a brief episode of mouth sores and no symptoms or risk factors for a systemic illness probably require no testing. In people with several episodes of mouth sores, viral and bacterial cultures and various blood tests are done. A biopsy may be done for persistent sores that do not have an obvious cause.

Eliminating foods from the diet one at a time or changing brands of toothpaste, chewing gum, or mouthwash can be useful to determine whether a specific food or mouth care product is causing the sores.

Treatment of Mouth Sores and Inflammation

  • Treatment of the cause
  • Avoidance of irritating foods and substances
  • Topical treatments

Doctors treat the cause, if known. For example, people are given antibiotics for bacterial infections. Avoiding any substances or drugs that are causing the mouth sores is recommended. Frequent, gentle toothbrushing with a soft brush and salt-water rinses may help keep sores from becoming infected.

Pain can be helped by avoiding acidic or highly salty foods and any other substances that are irritating.

Topical treatments

Topical treatments are substances applied directly to an affected part of the body. Topical treatments for mouth sores include

  • Anesthetics
  • Protective coatings
  • Corticosteroids
  • Burning with a laser or chemicals

An anesthetic such as dyclonine or lidocaine may be used as a mouth rinse. However, because these mouth rinses numb the mouth and throat and thus may make swallowing difficult, children using them should be watched to ensure that they do not choke on their food. Lidocaine in a thicker preparation (viscous lidocaine) can also be swabbed directly on the mouth sore.

Protective coatings containing sucralfate and aluminum-magnesium antacids can be soothing when applied as a rinse. Many doctors add other ingredients such as lidocaine and/or diphenhydramine (an antihistamine). Amlexanox paste is another alternative. Mouth rinses that contain alcohol (ethanol) should be avoided, because they may actually make the mouth sores worse.

Once doctors are sure that the sore is not caused by an infection, they may prescribe a corticosteroid rinse or a corticosteroid gel to be applied to each sore.

Some mouth sores can be treated with a low-powered laser, which relieves pain immediately and often prevents sores from returning. Chemically burning the sore with a small stick coated with silver nitrate may similarly relieve pain but is not as effective as a laser.

Key Points about Mouth Sores and Inflammation

  • A mouth sore that lasts more than 10 days should be evaluated by a doctor or dentist.
  • Isolated mouth sores in people with no other symptoms or risk factors for a systemic illness are usually caused by a viral infection or recurrent aphthous stomatitis.
  • Symptoms outside the mouth, a rash, or both suggest a more immediate need for evaluation.

More Information


Drugs Mentioned In This Article

Generic Name Select Brand Names
diphenhydramine No US brand name
sucralfate CARAFATE
lidocaine XYLOCAINE

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