Mouth sores can appear as blisters, open lesions (ulcers), inflammation or areas of skin discoloration. They may occur in a variety of locations in and around the mouth, including the lips, tongue, inner cheeks, gums, roof of the mouth (palate) or mouth floor.  

Mouth sores can occur due to a variety of causes. They may be the result of bacterial, viral or fungal infections. They may also stem from tissue injury (e.g., biting the lip or inner cheek) or chronic irritation (e.g., due to ill-fitting dentures, braces, tobacco or alcohol). Less commonly, mouth sores can occur as a result of immune system deficiencies, allergies, underlying medical conditions (e.g., cancer, autoimmune disorders), or as a side effect of certain medications.

Cold sores are one of the most common types of mouth sores. They usually appear outside of the mouth (e.g., on the lips) as blisters that ooze fluid and crust over. Cold sores can easily be passed from person to person. Canker sores are also very common, although they are not contagious and generally appear inside a person’s mouth. They are white or pale ulcers surrounded by a ring of reddened skin. Mouth sores can also appear as patches of white or gray skin inside the mouth, due to thrush or leukoplakia. 

Most mouth sores go away on their own within one or two weeks. However, patients should consult with a dentist or physician if they experience mouth sores that are severe, persist beyond two weeks or change in appearance.  

A dentist or other health care provider can usually identify the type of mouth sore by its location and appearance. Additional tests to detect or confirm the cause of mouth sores include x-rays, biopsies and blood tests.

Treatment generally focuses on alleviating the pain, discomfort or unpleasant appearance of mouth sores, and may include topical, oral or injectable medications. Other remedies include the use of mouth rinses and avoiding food and/or beverages that can irritate existing mouth sores.

There is no guaranteed method of preventing mouth sores. Because numerous factors can cause mouth sores, preventive techniques may depend on the specific condition causing the mouth sores. For example, antiviral medications may help prevent outbreaks of cold sores, but not canker sores.

In general, methods that may reduce the likelihood of developing mouth sores include practicing good dental hygiene, having regular dental examinations and exercising healthy eating habits, as well as avoiding potential irritants and people with contagious illnesses that can cause mouth sores.