Sores that occur in the mouth can take many forms. They may be open lesions (ulcers), raised bumps or blisters, inflamed areas or patches of discolored skin. They can appear in many different areas of the mouth, including the lips, tongue, inner cheeks, gums, roof of the mouth (palate), under the tongue or on the mouth floor.

Mouth sores may develop after the mucous membranes lining the mouth come into physical contact with an irritant. They may also appear as a result of infection, allergies or disease.

Normally, there are a number of bacteria, viruses and fungi that exist in the mouth. Many in saliva help to break down food particles while chewing. Many different factors (including conditions inside the mouth or irritating substances) can cause an overgrowth of these microorganisms. The bacteria, viruses or fungi then destroy tissue within the mouth – creating the ulcers, blisters, inflammation or discoloration that appear as mouth sores. Although it is not common, mouth sores may occasionally leave scars.

Most often, mouth sores last for one to two weeks then go away on their own without treatment. Occasionally, they may last for months.  

In people with immune system deficiencies, however, mouth sores can be severe and even life-threatening. Failure to properly treat mouth sores may result in the spread of infection, dental problems (e.g., abscessed teeth and gums) and, rarely, oral cancer.

Patients with mouth sores should consult with a dentist or physician in any of the following circumstances:

• Mouth sores have not healed after two weeks
• Sores are extremely painful or bleed
• Difficulty talking, chewing or swallowing occurs
• Other symptoms (e.g., fever, rash, drooling) appear
• There is a change in the appearance or nature of the sores