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It’s likely that at some point in your life, you’ve had a canker sore. In many cases, the sore clears up on its own after a few days or a week. While the occasional canker sore is one thing, recurrent aphthous stomatitis (RAS) can be even more bothersome.

RAS is the term used when canker sores keep coming back. Merck Manuals estimates that 20 to 30 percent of adults have recurring canker sores, and the condition is even more common in children. A study published in the International Journal of Orofacial Biology (IJOFB) notes that RAS is most common among people between the ages of 10 and 19. Some people may only have outbreaks a few times a year, while others may continuously have sores in their mouths, Merck Manuals notes.

What Does Recurrent Aphthous Stomatitis Look Like?

There are four forms of recurring canker sores, each with a slightly different appearance in the mouth.

  • Minor Aphthous Ulcers

    The most common form is minor aphthous ulcers, making up approximately 85 percent of all RAS cases, according to Merck Manuals. Usually, these sores are smaller than 8 millimeters across and usually clear up on their own within 10 days. The sores usually form on the floor of the mouth, the tongue or on the insides of the lips and cheeks.

  • Major Aphthous Ulcers

    Major aphthous ulcers are considerably less common than their minor counterpart and only occur in about 10 percent of cases. These sores are also bigger than minor aphthous ulcers — often more than 10 millimeters in diameter. They tend to take longer to heal, typically anywhere from a few weeks to a few months, and can be accompanied by fever and difficulty swallowing, explains Merck Manuals.

  • Herpetiform Aphthous Ulcers

    Herpetiform aphthous ulcers are even less common than major aphthous ulcers, accounting for 5 to 10 percent of RAS cases, according to the IJOFB study. These ulcers are more common in women than men and often develop in adulthood. Herpetiform sores are usually small and appear in clusters of anywhere from 10 to 100 sores. These clusters can develop all over the inside of the mouth and can lead to scarring.

  • HIV-Associated Ulcers

    Appearing as large lesions inside the mouth, HIV-associated RAS is the least common form of RAS and occurs in only about 2 to 3 percent of patients who are HIV-positive, as the IJOFB study notes.

Causes of Recurrent Canker Sores

The specific cause of recurring canker sores isn’t known, but it’s likely that one or more factors contribute to the condition. Both Merck Manuals and the IJOFB study note that the condition seems to run in families, meaning there may be a genetic link.

Possible causes of recurring canker sores range from certain medical conditions to nutritional deficiencies. Bacteria and viruses may play a role, but their exact contribution isn’t fully understood. Some factors that can contribute to recurring mouth sores include:

  • Nutritional Deficiencies

    People who have low levels of certain B vitamins, such as B12, or low levels of iron and zinc may be more likely to have recurring mouth sores, reports the IJOFB study. A review in The Journal of Clinical and Aesthetic Dermatology (JCAD) notes that in some cases, disorders such as celiac disease can contribute to nutritional deficiencies and recurring mouth sores.

  • Food Allergies

    Sometimes, an allergy or sensitivity to certain foods can trigger the development of canker sores, notes the IJOFB study. The ingredients found in some foods, such as dyes and preservatives, may also play a role.

  • Inflammatory Bowel Disease

    Up to 20 percent of patients with Crohn’s disease have mouth lesions, as the JCAD review explains.

  • Behcet’s Disease

    Recurring lesions in the mouth are usually one of the first signs of Behcet’s disease, which is a condition that often leads to the development of lesions on the skin and in the mouth and also causes problems in the eyes. The National Center for Advancing Translational Sciences notes that Behcet’s disease is more common in Turkey, Japan and Israel and less common in the U.S.

  • Medications

    Some medications, such as certain antibiotics, chemotherapy drugs or anti-seizure medications may contribute to recurring canker sores, according to the JCAD review.

  • Psychological Conditions

    A study in the Journal of Oral Pathology & Medicine found that symptoms of RAS were strongly associated with anxiety, depression and stress.

  • Viruses and Bacteria

    While viruses don’t cause canker sores the same way they cause cold sores, they may play a role in the development or recurrence of the sores, reports the IJOFB study.

Coping With Recurrent Canker Sores

Your dentist and doctor can work with you to help you manage and treat recurring canker sores. The Mayo Clinic notes that mouthrinses or topical gels can be used to help ease discomfort. Depending on the cause of the sores, your best option may be to treat the underlying condition or avoid the foods that trigger it. While the sores are certainly uncomfortable, know that RAS affects up to a third of the population, and your dentist or doctor can help you ease and treat your symptoms.