Canker Sores: What to Know About These Painful Mouth Sores

Yes, they hurt. Here are the symptoms, risks, triggers, and treatments for canker sores, which may help you stop the pain fast.

If you’ve ever gotten a painful, white patch on the inside of your mouth—also known as a canker sore or aphthous ulcer—you’re certainly not alone. About one in 10 people have gotten this type of mouth sore, making it one of the most common oral problems, according to the Institute for Quality and Efficiency in Health Care. To help you figure out if what you’re experiencing is indeed a canker sore—and how to get rid of it—we spoke with experts about the symptoms, causes, and treatments of canker sores,. Here’s what you need to know about canker sores. (And here are 11 reasons you really need to take care of your teeth.)

Canker sore symptoms

Medically known as aphthous ulcers, canker sores come in three types—minor, major, and herpetiform, explains Kyle Jones, DDS, an oral and maxillofacial pathologist and assistant professor at the University of California San Francisco’s School of Dentistry. Minor aphthous ulcers are the most common, and they usually show up in the size of about 0.3 to one centimeter (about 0.39 inches) and last anywhere from seven to 14 days. Major aphthous ulcers are bigger (as the name suggests), and can be one to three centimeters in size (which is just over one inch). These can take up to six weeks to heal.

Many times, you’ll also get a scar from these larger sores. (Jones recommends calling a doctor if your canker sore lasts longer than two weeks, and typically, people who have these large sores will do so anyway as they can be super painful.)

Despite the name, herpetiform aphthous ulcers have nothing to do with the herpes virus. They’re small in size (0.1 to 0.3 millimeters), but they tend to appear as a group of up to 100 ulcers, Jones says. They usually heal in about seven to 10 days.

With all of these types of ulcers, people will experience symptoms that include burning, itching, or a stinging sensation where the sore pops up, usually presenting with a small red patch before the yellow or white ulcer forms, Jones says.

Canker sores also tend to be more common in younger people, usually in those under the age of 25 or 30, says Thomas Sollecito, DMD, professor and chair of the department of oral medicine at Penn Dental Medicine. When you get into your 40s or older, they usually occur much less frequently.

close up of woman showing canker sore inside mouthp_saranya/Getty Images

Canker sore causes

Many things can cause a canker sore, though experts aren’t 100% sure of the exact mechanisms in the body that trigger them. Sometimes it’s trauma to the mouth—say if you cut yourself, says Sollecito.

Other times, you won’t experience trauma, but you will have some sort of immune reaction. “The formation of the ulcers themselves seem to be due to T cells in the immune system that lead to a destruction of the overlying epithelial cells [cells on the skin],” says Jones. He says there are likely a few other immune reactions involved, too. (Learn why 20 minutes is the magic number for a healthier immune system.)

“The cause appears to be different things in different people—it’s very variable,” Jones explains. “You have to sort of figure out [the triggers] yourself… The end results look similar, but there are a lot of different roads that can get you there.”

Canker sore triggers to avoid

People can experience a wide range of things that can trigger canker sores, ranging from certain foods to elevated stress levels. Some people might have a sort of allergic reaction to foods like citrus fruits, chocolate, nuts, milk, or gluten, says Jones. Often times it can be acidic foods in general, says Inna Chern, DDS, a New York City-based dentist.

Others might get them from certain food preservatives or toothpaste ingredients like sodium lauryl sulfate, or even from certain medications, like nonsteroidal anti-inflammatory drugs or beta-blockers. Quitting smoking can also occasionally cause canker sores to arise soon after you stopped. And to top it off, mental and physical stress can cause an outbreak, too.

Genetics also plays a strong role, according to the experts we spoke with. So, if your parents or siblings tend to get canker sores often (or they did when they were younger), you’re likely to, as well.

What’s the difference between a canker sore and cold sore?

Canker sores often get confused with cold sores, mainly because they both occur in the mouth and present with similar symptoms. But there’s a big difference between the two: “A canker sore is something that’s related to an immunologic change within the tissues within the mouth,” says Sollecito. “Cold sores are caused by a virus. So, one is viral-related, another is an immune reaction.”

The virus in this case is usually a herpes simplex virus (often herpes simplex virus type 1, or HSV-1).  That means that while cold sores come from a herpes virus infection, canker sores do not. (By the way, here’s how to curb sun-related herpes outbreaks.)

In terms of the differences in symptoms between canker sores and cold sores, you’ll typically get canker sores on areas of the mouth like the inside the cheeks, the inner wet surface of the lips, underneath the tongue, or on the floor of the mouth, Jones says. (Skin that’s more moveable in the mouth is more susceptible.) Cold sores, on the other hand, often occur on the gums, the roof of the mouth, the top of the tongue, or where the lip meets your facial skin.

Another key difference: Cold sores will start with little blisters that will rupture. “Once they rupture, they’ll come together into one larger or a few ulcers,” says Jones. “Canker sores don’t do that. You may start out with a little patch. But you won’t have a fluid-filled blister.” (Here are 12 cold sore remedies you can make at home.)

woman gargling and rinsing with waterAndreyPopov/Getty Images

Canker sore treatments

Once you know the difference between a canker sore and a cold sore, you can better know how to treat it. There are several things you can do if you get a canker sore. First off, try cleaning out the mouth with a mix of water and salt, Jones suggests. (Try 1 tsp in an 8-ounce cup of room temperature or warm water.) Rinse for about one to two minutes and then spit out. You can do this after meals or anytime throughout the day.

An over-the-counter topical anesthetic will also numb the area, helping to alleviate the pain—though this won’t necessarily treat the actual ulcer, says Sollecito. You’ll often find benzocaine (sold as Orajel) on store shelves. Here are a few other ideas for how to stop canker sore pain.

“Depending on where the sore is, it may take longer to heal if it is in a very ‘mobile’ part of the mouth and will require constant application of the numbing cream,” says Chern, who suggests you avoid acidic or bitter foods and beverages while the sore is trying to heal. “There is no way to completely avoid a canker sore but addressing it the minute it comes into the mouth is key—avoid anything that will exacerbate it, such as trauma from aggressive toothbrushing and acidic foods or beverages. This is crucial in limiting the duration that it stays in the mouth.”

If you treat the canker sore early with a topical steroid—you’ll need a prescription from your doctor—that can make the canker sore go away faster, Sollecito adds. This is a common treatment for the condition, but one that does require a visit to a healthcare professional. Chern says she also treats canker sores in-office with laser therapy, called Diode, and a topical treatment known as Debacterol, a sulfuric acid-based drug, which addresses the pain these canker sores can cause.

If someone is getting canker sores very often, and they’ve out ruled underlying issues, sometimes doctors will recommend systemic medications (ones that you likely ingest), but those are for more serious cases, Sollecito says.

When to see a doctor

In most cases, you don’t need to see a doctor for a canker sore. However, if you used to get canker sores when you were younger, then they went away, and now you’re older, and all of a sudden you seem to get them consistently, it might be time to talk to your doctor, says Sollecito. Also, if you’ve had one for two weeks, it might be time to call in a professional, Jones adds.

For the most part, though, canker sores are a minor health problem—and likely, your body will take care of it on its own, according to experts. In rare cases (again, particularly if you’re older and all of a sudden get frequent canker sores) it could be the sign of a more serious issue.

When a canker sore can signal a serious problem

Many illnesses can cause canker sores, which means yes, occasionally, this type of oral issue can be the sign of a more serious problem, Sollecito explains. For example, celiac disease, irritable bowel syndrome, anemia, or immune-compromising conditions like HIV/AIDS can all lead to canker sores. Sometimes these ulcers can also be a sign of a vitamin or mineral deficiency, most commonly a B12 or iron deficiency. A simple blood test from your doctor could help rule these factors in or out, Sollecito says. This will help you figure out the next steps you need to take to address both the canker sores and the underlying health condition.

Keep in mind that on average, canker sores are minor issues (even if they’re super painful). “For most people, they will resolve in a couple of weeks,” says Jones. “But if you’re concerned, reach out to a doctor like your physician or dentist. If you’re getting them more frequently, and it’s affecting your quality of life, definitely reach out to a professional.”

  • Institute for Quality and Efficiency in Health Care: "Canker sores (mouth ulcers): Overview"
  • Kyle Jones, DDS, PhD, an oral and maxillofacial pathologist and assistant professor at the University of California San Francisco's School of Dentistry. San Francisco
  • Thomas Sollecito, DMD, professor and chair of the department of oral medicine at Penn Dental Medicine, Philadelphia
  • Inna Chern, DDS, dentist at New York General Dentistry, New York City
Medically reviewed by Jessica Wu, MD, on May 28, 2020