Most canker sores last one to two weeks and heal on their own without scarring. The exact timeline depends on which type you have. Minor canker sores, which account for the vast majority of cases, typically resolve within 10 to 14 days. Major canker sores can take up to six weeks.
Healing Times by Type
There are three types of canker sores (also called aphthous ulcers), and each follows a different timeline.
Minor canker sores are the most common. They’re small, oval-shaped, and appear on the soft tissues inside your mouth, like the inner cheeks, lips, or under the tongue. They heal without scarring in one to two weeks.
Major canker sores are larger, deeper, and affect roughly 10% of people who get recurrent canker sores. These can take up to six weeks to heal and often leave scars. If you have a sore that’s unusually large or deep, this is likely the type you’re dealing with.
Herpetiform canker sores are the rarest type. They appear as clusters of tiny sores that can merge into one larger ulcer. Despite their more dramatic appearance, they heal in one to two weeks without scarring, similar to the minor type.
What the Healing Process Looks Like
Before a canker sore fully appears, many people notice a tingling or burning sensation in the spot where it’s forming. This prodromal stage can last a day or two. The sore then breaks open into a shallow ulcer, usually with a white or yellowish center and a red border. Pain tends to be worst during the first few days, especially when eating, drinking, or talking.
Over the next several days, the pain gradually fades and the ulcer begins to close from the edges inward. By days 10 to 14 for most sores, the tissue has fully resurfaced. You won’t see a scar from minor or herpetiform sores once they’ve healed. Major sores, because they penetrate deeper into the tissue, can leave visible scarring that persists.
What Can Slow Down Healing
Several factors can push a canker sore past the typical one-to-two-week window. Repeated irritation to the area is one of the most common culprits. Biting the inside of your cheek, brushing too aggressively near the sore, or eating sharp or acidic foods can reinjure the tissue and extend healing time. Braces, ill-fitting dentures, and rough dental work can do the same.
Nutritional deficiencies also play a role. Low levels of iron, folate, or vitamin B12 are associated with recurrent canker sores and slower recovery. One randomized trial found that topical vitamin B12 significantly reduced pain within two days of application, regardless of whether the person had a B12 deficiency to begin with. Correcting an underlying deficiency, if one exists, may help sores heal faster and recur less often.
A weakened immune system can dramatically extend healing times. In people with HIV, canker sores can persist for months rather than weeks. Other immune-suppressing conditions or medications can have a similar effect.
Canker Sores vs. Cold Sores
People often confuse canker sores with cold sores, but the two are different conditions with different causes. Canker sores appear inside the mouth on soft, non-keratinized tissue. They are not contagious and are not caused by a virus. Cold sores are caused by the herpes simplex virus, typically appear on or around the lips, and are contagious.
Both types generally resolve on their own within a similar timeframe. The key distinction is location: if the sore is inside your mouth on your cheek, tongue, or gums, it’s almost certainly a canker sore. If it’s on the outer edge of your lip or the skin around your mouth, it’s more likely a cold sore.
What Helps Them Heal Faster
No treatment makes a canker sore disappear overnight, but several options can reduce pain and may shorten healing time. Over-the-counter topical gels or pastes that contain a numbing agent can make eating and talking more comfortable. Anti-inflammatory rinses can also help reduce swelling in the tissue around the sore.
Avoiding triggers while the sore is active makes a noticeable difference. Spicy, acidic, or rough-textured foods can aggravate the ulcer and slow recovery. Switching to a soft-bristled toothbrush and using a toothpaste without sodium lauryl sulfate (a foaming agent linked to recurrent sores in some people) can reduce irritation.
For major canker sores or frequent outbreaks, prescription-strength topical treatments can help. These work by reducing the immune-driven inflammation that creates the ulcer in the first place.
When a Sore Lasts Too Long
A canker sore that lasts longer than two weeks warrants a visit to your doctor or dentist. That’s the clinical threshold where providers want to take a closer look. Most canker sores, even stubborn ones, resolve well before that point. A sore that lingers beyond two weeks could be a sign of a deeper issue, including a nutritional deficiency, an immune system problem, or in rare cases, oral cancer, which can mimic the appearance of a canker sore.
You should also seek evaluation if the sore is unusually large, if you’re getting canker sores very frequently, or if the pain is severe enough to interfere with eating and drinking to the point of dehydration or weight loss.