Canker sores are small, shallow lesions that develop on the gums, tongue and other soft tissues of the mouth, according to Mayo Clinic. Canker sores are not contagious and usually go away in a week or two. They can be painful, making talking or eating difficult at times.
Most canker sores are oval or round and have a white or yellow center ringed in red, Mayo Clinic reports. Some patients notice a burning or tingling sensation a day or so before the sore appears. Unlike cold sores, canker sores are not associated with the herpes virus.
The most common canker sores are minor and heal without scarring within two weeks, notes Mayo Clinic. Major canker sores are larger and deeper than minor canker sores and are very painful. They are usually round and may have irregular edges if they are very large. Major canker sores can take up to six weeks to heal and can cause significant scarring.
Herpetiform canker sores are uncommon and usually develop in older adults, Mayo Clinic explains. They are pinpoint-sized sores that appear in clusters ranging from 10 to 100. Typically, herpetiform canker sores disappear within two weeks without scarring.
A doctor should be consulted if fever is present or the sore is very large or very painful, Mayo Clinic advises. If a canker sore does not heal within a couple of weeks or outbreaks are frequent, patients should see a doctor.