A canker sore on your gums is a small, shallow ulcer that forms on the soft tissue inside your mouth. These sores are round or oval, typically white or yellowish in the center with a red border, and they can make eating, drinking, and brushing surprisingly painful. They’re one of the most common oral conditions, and while they’re not contagious or dangerous, they can be a recurring nuisance for some people.
What a Canker Sore Looks and Feels Like
Canker sores have a distinct appearance: a shallow, well-defined oval with a yellowish-gray center surrounded by a red halo and slightly raised red edges. That gray center is a thin layer of dead tissue the body is actively working to replace. On the gums, they tend to appear along the gum line near the base of your teeth or on the inner surface of the gums facing your cheeks or lips. The pain usually peaks in the first few days, then gradually fades as the sore heals.
One detail that helps with identification: canker sores only form inside the mouth. Cold sores, by contrast, appear on the outside of the mouth, typically around the border of the lips. Cold sores are caused by a virus and are contagious. Canker sores are neither viral nor contagious. If you have a painful spot on the inner surface of your gums, cheeks, lips, or tongue, it’s almost certainly a canker sore rather than a cold sore.
Three Types, Different Timelines
Not all canker sores behave the same way. The type you have determines how long you’ll be dealing with it.
- Minor canker sores are the most common. They measure less than one centimeter across (smaller than a pea) and heal within a few weeks without leaving a scar.
- Major canker sores are larger than one centimeter, extremely painful, and can take months to heal. These often leave scars behind.
- Herpetiform canker sores are tiny, pinpoint-sized sores that appear in clusters. Despite the name, they have nothing to do with the herpes virus. They typically heal within about two weeks and don’t scar.
Most people who get canker sores on their gums are dealing with the minor variety, which resolves on its own.
What Triggers Them
Canker sores don’t have a single cause, which is part of what makes them frustrating. Several overlapping factors can set one off.
Physical irritation is one of the most common triggers on the gums specifically. A slip of the toothbrush, a sharp chip, braces, or an ill-fitting dental appliance can break the surface of the gum tissue and invite a sore to form. Acidic or spicy foods can also irritate the soft tissue enough to start the process.
Your toothpaste may play a role. A foaming agent called sodium lauryl sulfate (SLS), found in most commercial toothpastes, has been linked to more frequent canker sores, greater pain intensity, and longer healing times. In one double-blind crossover study, people who brushed with SLS-containing toothpaste developed significantly more sores than those using an SLS-free alternative. If you get canker sores regularly, switching to an SLS-free toothpaste is one of the simplest changes you can try.
Stress and lack of sleep are well-recognized triggers, though the exact mechanism isn’t fully understood. Hormonal shifts, particularly around menstruation, also increase susceptibility in some people.
Nutritional Deficiencies
Recurring canker sores sometimes signal that your body is low on certain nutrients. In a study of 273 people with recurrent canker sores, about 20% were anemic, 20% had low iron levels, nearly 5% were deficient in vitamin B12, and about 3% were low in folate. These aren’t dramatic numbers, but they’re high enough that persistent sores, especially ones that keep coming back every few weeks, are worth mentioning to your doctor. A simple blood test can check for these deficiencies, and correcting them often reduces how frequently sores return.
How to Manage the Pain at Home
Most minor canker sores heal on their own, but the first several days can be genuinely miserable, especially when the sore sits right where your toothbrush or food hits the gum. A few strategies can speed healing and cut the pain.
A saltwater rinse is the simplest and most effective home remedy. Mix one teaspoon of salt into eight ounces of warm water (use half a teaspoon if the rinse stings too much at first). Swish gently for 30 seconds and spit. The salt raises the pH inside your mouth, shifting it from acidic to alkaline. Bacteria that contribute to inflammation thrive in acidic conditions, so this shift creates a less hospitable environment and helps the tissue heal faster. Rinsing two to three times a day, especially after meals, makes a noticeable difference for most people.
Over-the-counter oral gels containing a numbing agent can temporarily dull the pain before meals. Applying a small amount directly to the sore creates a protective barrier between the ulcer and whatever you eat or drink. Avoid crunchy, acidic, or very salty foods while the sore is active, as these will irritate the exposed tissue and prolong healing.
When Treatment Goes Beyond Home Care
For major canker sores or sores that recur frequently, a dentist or doctor may prescribe a steroid paste that you apply directly to the sore. These work by reducing the inflammatory response at the site, which shrinks the sore faster and lowers pain. The paste is typically applied after meals and at bedtime using a cotton swab. You press a thin film onto the sore rather than rubbing it in, since rubbing causes the paste to crumble.
Prescription-strength rinses containing anti-inflammatory or antimicrobial ingredients are another option for people who develop multiple sores at once or who can’t easily apply paste to hard-to-reach spots on the gums.
Signs That Need Attention
A typical canker sore, even a painful one, follows a predictable pattern: it shows up, hurts for a few days, and heals within two weeks. Certain features break that pattern and warrant a closer look.
Any sore in the mouth that persists for more than two weeks without improvement should be evaluated by a dentist or doctor. Sores that interfere with your ability to eat or drink, sores larger than a centimeter, sores accompanied by a high fever, or sores that keep returning in rapid succession all fall outside the range of a normal canker sore. In some cases, a persistent ulcer may need a biopsy to rule out other conditions. This is uncommon, but it’s the reason the two-week rule exists: most canker sores are well on their way to healing by that point, and one that isn’t may be something else entirely.
Recurring canker sores can also be a feature of certain systemic conditions, including celiac disease, inflammatory bowel disease, and immune disorders. If you’re getting sores frequently and also experiencing digestive symptoms, fatigue, or unexplained weight loss, those details together paint a fuller picture for your doctor to work with.