On average, how long will a canker sore usually last?

Varies: The severity and duration of canker sores varies greatly from person to person: it could be a few days or a few weeks. Try to do things to build up your immune system and avoid thing that will weaken it.

8-12 days: Most canker sores ate caused by a viral entity with a specific duration. You should be examined by a professional.

Aphthous ulcer?: There seems to be some confusion among patients regarding the difference between a canker sore (ahphous ulcer) whose cause is not well understood but often related to stress and local irritation vs. A cold sore (herpes) lesion caused by a virus. They appear differently and also tend to occur in different locations (intraorally vs the outside of the lips). 7-14 days for canker sore.