Roll your tongue around your mouth, and you might feel a sting from a new tender spot. A tiny, unwelcome crater of pain, a red circle of fire tucked against your cheek. It feels worse with every prodding poke.Another canker sore. What did you do to deserve this?Maybe nothing at all. “Most times, we don’t know why they come,” says Dr. Alessandro Villa, chief of oral medicine and oral oncology at Miami Cancer Institute at Baptist Health South Florida. Humans have figured out the forces behind planetary motion and the Irish potato famine, yet most canker sores remain something of a mystery, even while affecting 25% of people worldwide. [time-brightcove not-tgx=”true”]Although a single cause hasn’t been identified, we do know that these sores, also known as ulcers, can coincide with serious health problems. Here’s a guide to distinguishing a trivial canker sore from one with deeper significance, along with strategies for treatment and prevention.Meet the common canker soreUsually a canker sore is nothing to write home about. In minor cases, they appear infrequently, maybe once every three months. They’re only slightly painful, just enough to be annoying, Villa says. “The vast majority of canker sores are just canker sores,” agrees Dr. Herve Sroussi, associate professor of oral medicine at Harvard School of Dental Medicine.Minor canker sores should go away in a few days to a couple of weeks. Kids and young adults are most likely to develop them, especially when they’re under stress. This makes sense, Villa says, because canker sores seem related to immune system activity, and stress activates the immune system. “We don’t know if stress is the cause, but it could be a trigger,” he says. The sores are also associated with sleep deprivation, another challenge to immunity. Or they could pop up with “any illness that causes your immune system to misbehave,” like COVID-19 or a stomach flu, Sroussi says.Read More: 12 Weird Symptoms Dermatologists Say You Should Never IgnoreBut the stressor doesn’t always involve the immune system. People can get canker sores just from biting their cheeks. “Typically a little laceration will heal, but some people respond by getting an aphthous ulcer,” Sroussi says, using the scientific term for a canker sore. Simply try chewing more carefully. “This kind of lifestyle modification is definitely part of the treatment,” Sroussi explains. Foods that irritate the mouth could be another culprit, particularly crunchy, spicy, or acidic ones. Researchers haven’t confirmed this effect, though these foods certainly make an existing canker feel worse.A surprising factor in some cases is toothpaste. A foaming agent called sodium lauryl sulfate is a common ingredient that can disrupt the cheek’s protective barrier in people susceptible to mouth ulcers, some research shows. “It might cause a tingly, burning mouth after brushing,” leading to canker sores, says Dr. Fazia Mir, a gastroenterologist in Albuquerque, who treats patients with these ulcers. Finding a brand without this ingredient could be your solution.More than annoyingOther types of canker sores are more painful, turning eating into an act of self-torture. Compared to minor canker sores, so-called “major” cankers are larger and occur more often. “It’s to the point where the patient is never ulcer free, and it affects their quality of life,” Sroussi says. Major cankers call for a doctor visit, as they’re linked to chronic underlying diseases in many cases.In addition to major canker sores, another serious type is sometimes described as severe or complex. It’s the one most associated with an underlying condition. Patients with these severe cankers, often women, have many tiny ulcers in their mouth at the same time. “It’s debilitating,” Villa says, interfering with eating, speaking, and swallowing.Yet another subtype is herpetiform ulcers, which resemble but differ from herpes. The common denominator of these more problematic mouth ulcers is that they hurt more and last longer than the minor version, and they occur with other symptoms. “They’re red flags of a larger issue, where the mouth is just mirroring what’s happening on a systemic level,” Villa says. Upon visiting your primary doctor, you’ll probably be referred to a dentist, especially if you didn’t have cankers as a kid or young adult. Rule out oral cancerA dentist or oral medicine specialist will inspect the spot to make sure it’s not oral cancer. “What we really worry about with debilitating canker sores, especially if the patient uses tobacco or alcohol, is that it’s the first presentation of a malignancy,” Mir says.In some instances, dentists can tell if it’s malignant or benign just by looking. Common cankers usually live inside the cheeks or lips; a sign of a more troubling issue is if the spot resides elsewhere, like on the gums, side of the tongue, or floor of the mouth. Most oral cancers are bumpier than ordinary cankers. However, “major cankers can resemble cancer of the mouth,” Villa says. When the eye test isn’t definitive, a biopsy may confirm the diagnosis.It’s unlikely to be cancer, particularly in younger people. “If you’re under 20, I’ll think it’s either a nutritional deficiency or gastrointestinal health,” Mir says.The canker is trying to warn youAssuming it’s not cancer, a very painful and frequent canker sore may indicate another chronic problem to be explored and addressed. Several underlying conditions are associated with canker sores.Poor nutrition is sometimes involved. “There’s pretty strong data to support that nutritional deficiencies could be a causative factor for canker sores,” Villa says. Mir tells some patients to take a zinc supplement. Other nutrients that may play a role include ferritin, folate, and B12. A preliminary study last year found a connection between canker sores and vitamin D deficiency. Not enough antioxidants in your diet is another potential factor, research shows. “If you’re eating a lot of ultra-processed food, or you’re in a nutritional desert, then by all means, it’s important to look at diet,” Mir says.Read More: Why One Dietitian is Speaking Up for ‘Ultra-Processed’ FoodsThe sore will likely go away—and reoccur—before one’s diet or supplements can fix the deficiency. The corrective process can take months. “It’s probably going to come back until the deficiency is addressed,” Mir explains. Aside from nutrition, cankers are also linked to a range of autoimmune disorders like Crohn’s and celiac disease. A rarer autoimmune condition, Behcet’s disease, features painful cankers. Because these diseases may affect the intestines as well, they can present with digestive issues—such as ulcerative colitis, irritable bowel syndrome, and colon ulcers—in addition to the mouth ulcers. Inflammation throughout the body could also contribute to canker sores. “Inflammatory markers are overexpressed in patients with aphthous ulcers,” Villa says.Yet another condition linked to cankers is a syndrome called periodic fever, adenopathy, pharyngitis (PFAPA) syndrome. In addition to cankers and fevers, patients may get swollen lymph nodes.Not everyone develops canker sores due to these conditions. Some are more susceptible; researchers have found certain genes associated with mouth ulcers. “It’s clear that genetic background puts people at higher risk,” Sroussi says. How to treat and prevent canker soresSeveral treatments can help, and they’re especially effective when started as early as possible. For a minor canker, you probably don’t need a prescribed medication. Before all else, try home remedies: swab a mix of water and hydrogen peroxide onto the sore several times per day, or rinse with warm water and salt. This should ease some discomfort. “I get my little canker sore here and there,” Villa says. “It’s annoying, but I’m not taking a steroid for it.”Major or complex ulcers are another story. In these more painful situations, a topical corticosteroid can be rubbed onto the canker to soothe the area. A physician may prescribe stronger steroids in pill form. The most common example is prednisone. Other steroids like triamcinolone can be injected directly into the lesion. “This works well for ulcers that are really deep and painful,” Sroussi notes. For all steroid types, Sroussi recommends against prolonging their use, due to potential side effects. Read More: The Healthiest Way to Clean Your HouseA drug typically given for psoriasis, called apremilast, provides an anti-inflammatory effect without the immune suppression of steroids, Sroussi says. In a recent pilot study, apremilast caused “rapid and sustained” improvements. Especially bad cankers may be treated with a medication called CellCept, which does suppress the immune system to bring down inflammation—but only if all else fails. Over-the-counter gels provide temporary pain relief for both minor and moderate cankers. They feature an anesthetic called benzocaine that numbs the affected area. They also shield the canker from irritating food. However, these gels won’t necessarily make the sore go away.Prescription mouthwashes can help. Mir recommends Magic Mouthwash to her patients. It’s a cocktail of canker remedies like lidocaine, which is a local anesthetic, and antihistamines. Other mouthwashes for cankers are single-ingredient antimicrobial rinses.More therapies are in the works. A Swedish startup called Mucocort is developing a biodegradable patch that goes over the canker sore with the goals of protection, pain relief, and healing. A clinical trial is set to begin soon. Other research supports such patches, as well as laser and freezing therapies.Of course, if a patient is found to have an underlying condition, the priority is treating the condition, which may address the cankers, too.Don’t forget nutrition. Sroussi recommends keeping a diary to track which foods seem to incite cankers. As always, regular brushing and flossing are important. Canker sores are associated with certain mouth bacteria.If they really torment you, consider keeping a broader diary to identify other activities that reliably coincide with cankers, and try to avoid them. If the behavior is necessary, like stressful work or lost sleep during an international flight, Sroussi sometimes prescribes swish-and-spit steroids to stop cankers in their tracks, before people even get them. “Prevention is a possibility,” he says.