Mouth sores vary in appearance and size and can affect any part of the mouth, inside and outside. Some sores may be raised, usually filled with fluid (in which case they are called vesicles or bullae, depending on size), whereas others may be ulcers. An ulcer is a hole that forms in the lining of the mouth when the top layer of cells breaks down and the underlying tissue shows through. An ulcer appears white because of the dead cells and food debris inside the hole.
There are many types and causes of mouth sores. Because the normal flow of saliva helps protect the lining of the mouth, any condition that decreases saliva production makes mouth sores more likely. Any sore that lasts for 10 days or more must be examined by a dentist or doctor to ensure that it is not cancerous or precancerous (see Mouth Growths: Overview of Mouth Growths).
Injury or irritation:
Any type of damage to the mouth, for instance, when the inside of the cheek is accidentally bitten or scraped by 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. Noncancerous ulcers are always painful until healing is well under way.
Many foods, drugs, and chemicals can be irritating or trigger a type of allergic reaction, causing mouth sores. Acidic foods may be particularly irritating, as can certain ingredients in common substances such as toothpaste, mouthwash, candy, and gum. The most common drugs causing mouth sores include certain cancer chemotherapy drugs and drugs containing gold.
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 Viral Infections: Herpes Simplex Virus Infections), are perhaps the most well known. Herpes zoster, the virus responsible for chickenpox as well as the painful skin disorder called shingles (see Viral Infections: 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. Herpes zoster is treated much like severe herpes simplex, but occasionally the mouth may remain painful for months or years or even permanently after the sores have healed.
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. Bacterial infections from teeth or gums can spread to form a pus-filled pocket of infection (abscess) or cause widespread inflammation (cellulitis). Bacterial infections that spread from decayed lower teeth to the floor of the mouth can cause a very severe infection underneath the tongue called Ludwig's angina. The swelling caused by this infection may force the tongue upward and block the airway. Infections from an upper tooth can spread to the brain.
Syphilis may produce a red, painless sore (chancre) that develops in the mouth or on the lips during the early stage of infection (see Sexually Transmitted Diseases: 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.
Behçet's syndrome, an inflammatory disease affecting many organs, including the eyes, genitals, skin, joints, blood vessels, brain, and gastrointestinal tract (see Vasculitic Disorders: Behçet Syndrome), 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 sprue, 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 as well, although most of the time these sores are not as uncomfortable as those on the skin (see Psoriasis and Scaling Disorders: Lichen Planus). Pemphigus vulgaris (see Blistering Diseases: Pemphigus Vulgaris) and bullous pemphigoid (see see Blistering Diseases: Bullous Pemphigoid), both skin diseases, can also cause blisters to form in the mouth.
Canker sores are one of the most common causes of mouth sores. Their cause is unknown.
An uncommon condition called necrotizing sialometaplasia may begin after an injury to the mouth. In this condition, a large, gaping sore up to 1 inch (about 2½ centimeters) in diameter forms on the roof of the mouth within 1 or 2 days of an injury. Despite its unsettling appearance, necrotizing sialometaplasia is relatively painless and heals without treatment in 1 to 3 months. A doctor may distinguish the condition from oral cancer based on the symptoms (cancer would take a long time to reach the same size and by then would be painful) and sometimes by performing a biopsy (removing a tissue sample for examination under a microscope).
Doctors treat the cause, if known. Frequent, gentle toothbrushing with a soft brush 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. 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. Sucralfate and aluminum-magnesium antacids can be soothing when applied alone, but many doctors mix them with a combination of lidocaine, diphenhydramine (an antihistamine), and kaolin to form a rinse. Amlexanox paste is another alternative.
Once doctors are sure that the sore is not caused by an infection, they may prescribe 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 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.
Last full review/revision October 2006 by Robert B. Cohen, DMD