Cedars-Sinai Blog

Everything You Ever Wanted to Know About Canker Sores

canker sore, blister, mouth pain, tongue bump, cheek bump

Canker sores can have several causes or triggers.

Canker sores, also called aphthous ulcers, are small, painful sores that appear inside the mouth on the lips, cheeks, on the gums, and tongue.

They are appropriately named, too: In Greek, aphthae (root of aphthous) means "to set on fire."

Canker sores are not contagious and can’t be spread through saliva.

Most of us get canker sores from time to time; some of us get them over and over.

Either way, you want to get rid of them as quickly as possible. We talked to doctors to find out where canker sores come from, how to avoid them, and what to do if you get one.

Why do we get canker sores?

No one knows exactly what causes most canker sores, but we know they’re not contagious and can’t be spread through saliva.

They can be the result of an injury, like when you accidentally bite your cheek or when braces catch or rub against the inside of the cheeks or back of the lips, but often they appear seemingly out of nowhere.

They can be triggered by a number of things, like a weak immune system, dehydration, allergies, stress, and even medication.

Other common causes of canker sores:

Do I have a canker sore or cold sore?
What can I do about canker sores?

When to see a doctor about canker sores?