How do canker sores bleed ?

Canker sores: Canker sores are ulcers that are shaped like a crater and usually occur on the tongue, on the inside of the lips and cheeks, and the floor of the mouth. They do not usually bleed. Cold sores are groups of blisters that occur on the outside of the lips and around the mouth. They can break open and may bleed. Any sore that bleeds and has lasted for more than 10 days needs to be examined.

Canker sores: usually don't bleed. Canker sores are the most common oral lesions. Individual ulcers typically last 1-2 weeks. The condition is idiopathic (cause is not known) recurrent aphthous ulcers is usually self-limiting. If concerned see your dentist after 10 days.