"Canker sores" are painful ulcers on the inside of the cheek or tongue. They last up to 10 days and go away without any treatment, but they often return. Canker sores are common, affecting up to 40% of the population. In most cases, there are only 1 or 2 ulcers at a time.

The medical term for canker sores is "aphthous ulcers." Although the cause is unknown, a viral infection is suspected. They may also be genetic, as they seem to run in families.

Conditions associated with multiple, recurrent or longer-lasting aphthous ulcers include:

• Medications or toxins
• A reaction to certain foods (such as pineapple or nuts)
• Trauma
• Deficiency of certain vitamins (such as iron or vitamin B12)
• Celiac disease (also called sprue) in which there is a sensitivity to foods containing gluten (such as wheat)
• Infection with HIV or other viruses
• Crohn's disease (a form of inflammatory bowel disease)
• Behcet's disease (or syndrome), a disease thought to be due to a "misfiring" immune system that also causes similar ulcers in the genital area, rashes, eye inflammation, and arthritis

While a dentist, dermatologist or doctor may suspect Behcet's disease, a rheumatologist is the specialist who most commonly diagnoses and treats Behcet's disease. If you have eye inflammation, it's also important to see an ophthalmologist.

Talk to your doctor about your symptoms. He or she may recommend some tests or refer you to a specialist. The next steps depend on the details of your symptoms and results of your physical examination.