How do I know I have a canker sore?

Canker sores are small ulcers with a white or gray base and a red border; canker sores appear inside the mouth. They are not contagious, but can return frequently and may be only one canker sore or several. Their exact cause is uncertain but some experts believe that immune system problems, bacteria or viruses may be involved.

Canker sores are commonly mistaken for fever blisters or cold sores. The difference is in what causes them and their location. Fever blisters and cold sores are caused by the herpes simplex virus and may occur inside or outside the mouth as well as on the chin or in the nostrils. They often come back in the same location. Fever blisters and cold sores can be spread by kissing.

Canker sores are not contagious and only develop on the inside of the mouth. While both fever blisters and canker sores might look the same with a reddish, inflamed appearance, canker sores might also appear white and usually do not bleed. Younger women tend to get canker sores more often than older women.