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Most canker sores heal in 1 to 2 weeks without treatment, and major canker sores larger than 1 centimeter take up to 6 weeks. At Nova Dental, we tell patients that the pain and the sore run on separate clocks. Canker sore pain fades first, and two weeks is the point where we want to see any sore that has not closed.
A canker sore takes 1 to 2 weeks to heal when it is the minor type, which is the kind most people get. Size decides the rest. The clinical reference StatPearls puts minor sores at less than 5 millimeters across and major sores at more than 10 millimeters, and Mayo Clinic gives a healing time for each type.
For scale, 10 millimeters is about the width of a pea, so a major sore is one you would call large on sight. Mayo Clinic gives six weeks as the outer limit for major canker sores, and some clinical references put it longer.
Herpetiform canker sores have an alarming name and no connection to the herpes virus. The name only describes how the tiny sores cluster together.
Canker sore pain lasts a shorter time than the sore does. MedlinePlus, the National Library of Medicine's patient reference, says the pain often goes away in 7 to 10 days, while complete healing can take 1 to 3 weeks. The sharpest stretch is shorter still, with pain starting to ease within a few days.
Think of a scraped knee. The sting is gone by the weekend, and the scab hangs on for another week. A canker sore follows the same order, which is why a sore that has stopped hurting can still be visible.
Patients often read that quiet stretch as a problem. A sore that is painless and shrinking inside the first two weeks fits the normal pattern.
A canker sore moves through three stages: a warning stage, an open sore, and healing.
Warning stage. Mayo Clinic describes a tingling or burning feeling a day or two ahead of the sore. The feeling does not show up for everyone.
Open sore. A round or oval ulcer forms with a white or yellow center and a red border. Eating and talking are hardest during this stage.
Healing. The sore turns gray as healing starts, according to MedlinePlus, then gets smaller until the tissue closes.
A canker sore that is slow to heal has three common explanations: something keeps rubbing it, it is the major type, or the body is short on a nutrient.
Something keeps rubbing the sore. Mayo Clinic advises seeing a dentist about sharp tooth surfaces or dental appliances that seem to trigger sores. In our office the usual suspects are a rough filling edge, a chipped tooth, and a bracket or wire on braces. A sore scraped at every meal heals like a paper cut on a knuckle, reopening each time you bend it.
The sore is the major type. A sore wider than 10 millimeters runs on the longer clock in the table above, up to six weeks.
The body is short on a nutrient. Mayo Clinic links canker sores to low vitamin B-12, zinc, folate, or iron, and to conditions such as celiac disease and inflammatory bowel disease. A blood test ordered by a physician is how a deficiency gets confirmed, and our guide to why canker sores keep coming back covers those causes in detail.
A canker sore has lasted too long once it passes two weeks. Mayo Clinic, MedlinePlus, and the National Institute of Dental and Craniofacial Research (NIDCR) all draw the same line, and NIDCR advises seeing a dentist or doctor about any mouth sore present for more than two weeks.
A minor canker sore should be gone by then. One that outlasts two weeks is either the major type or a different kind of sore, and both call for an exam.
Canker sores are not cancer and do not cause cancer, as MedlinePlus states plainly. The two-week rule exists because a few other conditions can start out looking like an ulcer that will not close, and an exam is how they get told apart.
Any one of the signs below is a reason to call a dentist, based on guidance from Mayo Clinic, Cleveland Clinic, and NIDCR.
Red flags:
If you are on day 15 and unsure, count it as too long.
A dentist checks two things: what the sore is, and what keeps it from closing.
At Nova Dental, Dr. Talar Guldalian looks at the sore's size, edges, and location, then at everything that touches it. Sharp enamel, the margin of an old filling or crown, and the fit of a retainer or denture all get checked. She completed prosthodontics training at UCSF, which centers on how crowns, dentures, and other restorations fit against the mouth.
We use intraoral cameras to put the sore on a screen, so you see what we see. We also ask when the sore started, how often you get them, and which toothpaste you use.
When the pattern points toward a deficiency, we say so and recommend bloodwork through your physician. NIDCR notes that a dentist who finds anything unusual will recommend more tests or a referral to a specialist.
A routine exam already covers many of these checks, so mention any sore at your regular visit, even a small one.
A sore past the two-week mark deserves a look. Dr. Guldalian will examine it, show it to you on screen, and explain what she sees.
Nova Dental is independently owned, with no quotas behind the advice you get.
Yes, a few prescription treatments shorten a canker sore, though they do not change how often sores return. StatPearls reports that topical corticosteroids and chlorhexidine mouthwash reduce the severity of a sore and shorten its duration, with no effect on how often sores come back.
Corticosteroids and chlorhexidine are prescribed by a dentist or physician after an exam, and neither is the right choice for every sore. For occasional sores that clear in a few days, StatPearls notes that medication may not be required.
Over-the-counter numbing gels and gentle rinses are about comfort while the sore runs its course, and our guide covers ways to ease a canker sore at home.
Bring the timeline with you. Tell us when the sore started, where it sits, and whether it has shrunk, and we will take it from there.
We are at 304 Cambridge Road, Suite 340, Woburn, MA 01801, serving Winchester, Lexington, and Arlington. Call (781) 369-5722.
How long are canker sores contagious?
Canker sores are never contagious, so there is no contagious period to wait out. Mayo Clinic states that canker sores cannot be spread to other people and are not caused by a herpes virus. Cold sores, which are caused by a herpes virus, are a separate condition. Kissing or sharing a cup will not pass a canker sore along.
Do canker sores leave scars?
Minor canker sores usually heal without a scar, and they are the most common type. Herpetiform canker sores also heal without scarring. Major canker sores are deeper and wider than 10 millimeters, and Mayo Clinic notes they can leave scars. Scarring is one reason a large sore is better examined early than waited out.
How often do canker sores come back?
People prone to minor canker sores tend to get them again at intervals of 1 to 4 months, according to StatPearls. MedlinePlus advises contacting a provider if you get canker sores more than 2 or 3 times a year. Frequent sores are a reason to look for a cause, such as a rough tooth edge or a low vitamin level.
My canker sore doesn't hurt anymore but it's still there. Is that normal?
A painless sore inside the first two weeks is normal, because canker sore pain fades ahead of the sore. MedlinePlus puts pain at 7 to 10 days and full healing at up to 3 weeks. Once any mouth sore passes the two-week mark, NIDCR advises having a dentist or doctor look at it.
What does it cost to have a canker sore checked without insurance?
Patients who expect regular visits can look at our membership plan, which starts at $645 per year for an individual and includes exams, cleanings, and 15% off other procedures.