A small, shallow sore inside the mouth or at the base of the gums.
A canker sore is a small, shallow sore inside the mouth or at the base of the gums. Unlike a cold sore, it doesn't occur on the lips and isn't contagious.
It can be painful and make it hard to eat and talk.
Most canker sores clear on their own in 1 to 2 weeks. Treatments, if needed, include mouth rinses, pastes, and medication.