Most canker sores heal on their own within 10 to 14 days without any treatment. That timeline applies to the common, small variety that makes up the vast majority of cases. Larger or less common types can take significantly longer, and a few practical steps can influence how quickly you recover.
Healing Time by Type
Not all canker sores are the same, and the type you have determines how long you’ll be dealing with it.
Minor canker sores are the most common type by far. They measure less than 5 millimeters across (roughly the size of a pencil eraser or smaller), and they resolve within 10 to 14 days. They don’t leave scars. If you’ve had a canker sore before, this is almost certainly the kind you had.
Major canker sores are larger than 1 centimeter in diameter and go deeper into the tissue. These can take up to 6 weeks to heal and often leave a scar. They’re significantly more painful and can make eating difficult for the entire duration.
Herpetiform canker sores are the rarest and most severe type. They appear as clusters of tiny sores that can merge into larger, irregular ulcers. These persist anywhere from 10 to 100 days, and they make speaking and eating extremely difficult while they last. Despite the name, they have nothing to do with the herpes virus.
What the Healing Process Feels Like
In the first day or two, you may notice a tingling or burning sensation before the sore fully forms. This is the prodromal phase, and it’s your earliest warning sign. The sore then develops into a shallow, round or oval ulcer with a white or yellowish center and a red border. Pain typically peaks during this initial ulcerative stage, usually within the first three to four days.
After that peak, the pain gradually fades. A grayish membrane forms over the ulcer as the tissue starts to repair itself. By the end of the first week, most minor sores are noticeably smaller and far less painful. The final few days involve the sore flattening out and the surrounding tissue returning to its normal color. You generally won’t be able to tell where the sore was once it’s fully healed.
What Helps Them Heal Faster
Minor canker sores don’t require treatment, but several approaches can reduce pain and may shorten the healing window. Rinsing with salt water (about half a teaspoon of salt in a cup of warm water) helps keep the area clean and creates an environment that’s less hospitable to bacteria. It won’t dramatically speed healing, but it can prevent the sore from getting worse.
Over-the-counter topical gels and pastes that contain a numbing agent can make eating and drinking more comfortable. Applying them before meals is the most practical approach. For major canker sores or frequent outbreaks, a doctor may prescribe a topical corticosteroid to reduce inflammation and accelerate tissue repair.
While the sore is healing, avoiding acidic foods (citrus, tomatoes, vinegar-based dressings), spicy dishes, and crunchy or sharp-edged foods like chips and crackers makes a real difference in day-to-day pain levels. These don’t slow healing directly, but irritating the sore repeatedly can extend the inflammatory phase.
Preventing Recurrences
Canker sores are recurrent for many people, and one of the most evidence-backed prevention strategies is surprisingly simple: switching to a toothpaste that doesn’t contain sodium lauryl sulfate (SLS). SLS is a foaming agent in most commercial toothpastes, and a systematic review found that people who used SLS-free toothpaste had significantly fewer ulcers, shorter ulcer duration (about 2 fewer days per episode), fewer total episodes, and less pain compared to those using standard toothpaste. If you get canker sores more than a few times a year, this is the easiest change to try first.
Nutritional deficiencies also play a role. Low levels of B12, iron, and folate are all associated with recurrent canker sores. One clinical trial found that B12 supplementation reduced pain in people with aphthous ulcers regardless of whether their blood B12 levels were actually low to begin with, which suggests the benefit may extend beyond simply correcting a deficiency. A basic multivitamin or B-complex supplement is a reasonable step if you deal with frequent outbreaks.
Stress and minor mouth injuries (biting the inside of your cheek, aggressive brushing, dental work) are other common triggers. Soft-bristled toothbrushes and careful eating habits won’t eliminate canker sores entirely, but they reduce the mechanical irritation that often kicks off a new episode.
When Healing Takes Too Long
A canker sore that lasts longer than two weeks is worth having evaluated by a doctor or dentist. Most canker sores are harmless, but a sore that won’t heal on that timeline can occasionally indicate something else, including an infection, an autoimmune condition, or in rare cases, oral cancer. The same applies if you’re getting unusually large sores, running a fever alongside them, or finding that outbreaks are becoming more frequent or severe over time.