List of Diseases > Mouth Sores

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Mouth sores and inflammation (stomatitis) vary in appearance and size and can affect any part of the mouth, inside and outside. People may have swelling and redness of the lining of the mouth or individual, painful ulcers. An ulcer is a hole that forms 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. Some sores are raised and filled with fluid, similar to blisters (in which case 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.


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 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
  • 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

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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 (see Herpes Simplex Virus Infections) 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 (see 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 (see Syphilis). 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. Candidacan 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.

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The most common drugs causing mouth sores include certain cancer chemotherapy drugs. Drugs containing gold, which are used to treat rheumatoid arthritis and other autoimmune disorders, can also cause mouth sores, but these drugs are rarely used because safer and more effective drugs are now available to treat those disorders. 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 (see Behçet Disease), can cause recurring, painful mouth sores. Stevens-Johnson syndrome (seeStevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis), 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 (see Celiac Disease), which is caused by an intolerance to gluten (a component of wheat and some other grains), often develop mouth sores. Lichen planus (see 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 (see Pemphigus Vulgaris) and bullous pemphigoid (see Bullous Pemphigoid), both skin diseases, can also cause blisters to form in the mouth.


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.



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