Canker sores — a painful white sore inside the mouth — may be caused by stress. Or the wrong toothpaste. Or some foods: tomatoes, peanuts, cinnamon. or iron deficiency. or sensitivity. or a new prescription. or an underlying autoimmune disease.
Although millions of people suffer from them each year, researchers still don’t know much about the underlying causes of these sores. This leaves doctors and dentists stuck playing detective with their patients—running through a checklist, trying to figure out which of a dozen potential triggers could be causing the squeaky little lesions.
This list is long and includes different specialties in medicine. It includes oral trauma, stress, diet, genetics, hormones, allergies, vitamin deficiencies, autoimmune diseases, and gastrointestinal diseases. Mouth ulcers are multifactorial, which makes them difficult to study, Diana F. Massadi, a professor at the University of California, Los Angeles School of Dentistry, told me. Cold sores, by comparison, offer a more structured story: They are a viral infection (herpes simplex) and therefore treatable with antivirals. (Cold sores are pimple-like blisters that usually form around the lips, while canker sores are white sores that occur inside the mouth.)
Canker sores can be sorted loosely into buckets. In bucket A are the smaller and more common sores, the kind a person might get two or three times a year. These sores are blistering, uncomfortable, painful, and make eating and speaking difficult. It is usually not life threatening. In bullae B there are larger ulcers, usually more than 1 centimeter wide. (Technically, a third bucket contains sores that are herpetiform, or clustered, but this type is rare.)
Some large or small sores are associated with an underlying disease, such as Crohn’s disease, Behçet’s disease, HIV/AIDS, or celiac disease. In a way, these conditions are better understood: Sores are a byproduct of something else going on in the body—something a doctor can test for and identify.
The human mouth is a strange place. Canker sores occur in what’s called the oral mucosa, which is what doctors talk about the skin (not actually skin) inside your mouth. Even though the mucous membrane is located on the inside of your cheeks, it is exposed to a lot. Salsa, notes Nasim Fadel, a former professor at UC Davis who started the college’s Oral and Mucous Membrane Clinic, “is a chemical irritant. You don’t rub salsa on your skin.” But people do eat salsa — and chips, crackers, and other spicy, acidic, or sharp foods, which can damage the lining of the mouth. Some of these wounds later develop into canker sores.
Because the mouth is dirty, white blood cells love to be there; That way, they can respond quickly to potential infections, Andres Pinto, a professor at Case Western Reserve University’s School of Dental Medicine, told me. But sometimes, this monitoring system fails, and the body can actually harm itself. This is believed to be part of what causes typical canker sores, Pinto explained: immune dysregulation is the “common denominator” behind ulcers. Inflammation can help the body heal, but hyperinflation can cause mucosal rupture, which we see when we look at oval-shaped wounds.
Furthermore, canker sores are still idiopathic, which means doctors don’t really know why they occur. The body’s immune system is very complex. As my colleague Ed Young wrote in 2020, it’s the place “Intuition goes to die. “The problem with all of these immune-mediated conditions, more often than not, is that we still don’t know why they appear,” Alessandro Villa, MD, chief of oral medicine at the Miami Cancer Institute, told me. “At the end of the day, it’s still a huge mystery. “
Another long-standing mystery is why some people develop canker sores while others live in ignorant bliss, devoid of a certain kind of torture. Genetics are starting to help solve that. “With advanced computers, we can actually detect genes that are related to what we see in the mouth,” Pinto told me. “What I just said is a big step,” he added. “It probably took 30 years to develop that last sentence.”
More research is needed to improve treatment for patients, especially those with chronic or bad ulcers. Topical steroids can help, but they don’t treat the underlying causes. An FDA spokesperson told me that there are no FDA-approved prescription options specifically for canker sores.
In comparison, in the United States there aren’t a lot of service providers that specialize in this area. Fadell, formerly of the University of California, Davis, is a rare combination of dentist and dermatologist who occasionally sees patients with debilitating conditions. She told me, “I am on the same medications that I have been using for 10 years.” “It’s kind of sad.”
Oral therapists are dentists with additional training in such diseases. But Pinto estimates that only about 400 practice in the United States. A representative for the American Academy of Oral Medicine told me that the organization currently has 281 active members (though she notes that there may be other non-members practicing the treatment). For her part, Fadell believes dermatologists are better equipped to treat canker sores, because dentists “can’t prescribe the big guns.” (“The big guns,” in this case, are drugs that modulate the immune system to calm inflammation.) Even if the patient can see the right provider, this is only the first step. They will still need to go through the checklist, trying to determine what their triggers are – while the bigger question as to the cause of the sores remains unknown.
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