How Long Do Canker Sores Last? Healing Timeline

Most canker sores follow a predictable arc: the pain peaks early and fades within 7 to 10 days, and complete healing takes 1 to 3 weeks, according to MedlinePlus. The American Dental Association gives the same picture more briefly — one or two weeks, healing on its own. Large ulcers are the exception, and they run on a very different clock.

Three types, three clocks

Type	Share of cases	Size	Duration	Scarring
Minor aphthous	Over 70%	Under 5 mm	Within 2 weeks	None
Major aphthous	About 10%	Over 10 mm	5 to 10 weeks	Usual
Herpetiform	1% to 10%	2 to 3 mm, up to 100 at once	1 to 2 weeks	Infrequent

The minor type is what almost everyone means by “a canker sore”: one to six oval ulcers with a gray-white film and a red halo, recurring at intervals of one to four months. Herpetiform ulcers are the swarm — dozens of pinpoint sores, most often on the floor of the mouth and the tongue, which can merge into one irregular ulcer that does scar. Despite the name, StatPearls states plainly that they have no connection to herpes viruses; that comparison is spelled out in canker sore vs cold sore.

What drags the timeline out

Size is the dominant factor, but three others push a two-week sore into a three-week one:

• Repeat mechanical injury. A sore sitting where a tooth edge, bracket or denture rim touches it is reopened several times a day.
• Irritating food. Acidic, salty, crunchy and very hot items restart the inflammation each meal.
• An unresolved trigger. Where iron, folate or B-12 are low, new ulcers arrive before the old ones close, and the mouth never gets a clear week.

Two weeks is a decision point, not a suggestion

MedlinePlus is specific: contact a provider if the sore has not gone after two weeks of home care or is getting worse, if outbreaks come more than two or three times a year, or if the sore arrives with fever, diarrhea, headache or a rash. There is a second reason the two-week rule exists. Canker sores are neither cancer nor a cause of cancer, but some oral cancers first present as a mouth ulcer that simply does not heal — which is why persistence, not pain, is the signal clinicians act on.

Until then, the sensible target is comfort rather than speed; the measures worth trying are in how to relieve canker sore pain, and the reason they keep returning in recurring canker sores causes.

This content is informational and does not replace dental or medical consultation, diagnosis or treatment. See also canker sores in children.