Canker Sores
(Aphthous Ulcers)
Medical Authors: Siamak Nabili, MD, MPH,
and Dennis Lee, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
What are canker sores?
Canker sores are small ulcer craters in the lining of the mouth that are frequently painful and sensitive. Canker sores are very common. About 20% of the population (one out of five people) have canker sores at any one time. Canker sores are also medically known as aphthous ulcers or aphthous stomatitis.

Women are slightly more likely than men to have recurrent canker sores. It can occur at any age, but it is more commonly seen in teenagers. Genetic studies show that susceptibility to recurrent outbreaks of the sores is inherited in some patients. This partially explains why family members often share the condition.
Canker sores are generally classified into three groups based on size.
- Minor sores have a diameter of 1millimeter (mm) to 10mm. They are the most common (80% of all canker sores) and usually last about 7-10 days.
- Major sores (10% of all canker sores) have a diameter of greater than 10mm and they may take anywhere between 10-30 days to heal. They may leave a scar after they heal.
- Herpetiform ulcers (10% of all canker sores) are formed by a cluster of multiple small individual sores (less than 3mm). They also usually heal within 7-10 days.
What are symptoms of canker sores?
Canker sores are usually found on the movable parts of the mouth, such as the tongue or the inside lining of the lips and cheeks, and at the base of the gums. The ulcers begin as small oval or round reddish swellings that usually burst within a day. The ruptured sores are covered by a thin white or yellow membrane and edged by a red halo. Generally, the sores heal within
two weeks without scarring. Fever is rare, and the sores are rarely associated with other diseases. Usually, a person has only one or a few canker sores at a time.
Most people experience their first bout with canker sores between the ages of 10 and 20. Children as young as 2
years old, however, can develop the condition. The frequency of canker sore recurrences varies considerably. Some people have only one or two episodes a year, while others may have a continuous series of canker sores.
Next: What are the causes of canker sores? »
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