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Aches, Pains & Injuries

Canker Sores

About 1 in 5 people regularly get bothersome canker sores, which can make eating, drinking, and even brushing teeth a real pain. But just because they’re relatively common doesn’t mean these small open sores inside the mouth should be ignored.

About Canker Sores

Also known as aphthous ulcers, canker sores are small sores that can occur inside the cheeks and lips, at the base of the gums, and on or under the tongue.

But don’t confuse canker sores with cold sores or fever blisters, which are sores caused by the herpes simplex virus and found outside the mouth around the lips, on the cheeks or chin, or inside the nostrils. Whereas cold sores are contagious, canker sores are not contagious — so kissing cannot spread them.

Although canker sores aren’t contagious, the tendency to have outbreaks of canker sores can run in a family. No one knows exactly what causes canker sores, but many factors are thought to put a person at risk. Diet may play a part. People who have nutritional deficiencies of folic acid, vitamin B12, and iron seem to develop canker sores more often, as do those who have food allergies. Canker sores also can indicate an immune system problem.

Mouth injuries, such as biting the inside of the lip or even brushing too hard and damaging the delicate lining inside the mouth, also seem to bring on canker sores. Sodium lauryl sulfate (SLS), an ingredient in many toothpastes and mouthwashes, has been linked to canker sores and is thought to prolong the healing time of the sores.

Even emotional stress could be a factor. One study of college students showed that they had more canker sores during stressful periods, such as around exam time, than they did during less stressful times, such as summer break.

Although anyone can get them, young people in their teens and early twenties seem to get them most often, and women are twice as likely to develop them as men. Some girls and women find that they get canker sores at the start of their menstrual periods.

Signs and Symptoms

Canker sores usually appear as round, painful open sores that have a white or yellowish coating and a red “halo” around them. They tend to be small (¼ inch, or 6 millimeters across) and shallow, but occasionally they might be larger and deeper. Most often, canker sores pop up alone, but can also occur in small clusters. Sometimes an area will tingle or burn before a canker sore actually develops.


Canker sores usually are not accompanied by other symptoms (like fever or swollen lymph nodes). If they are, this could be a sign of another condition that should be checked out.

It takes about 2 weeks for canker sores to heal. During this time, the sores can be painful, although the first 3 to 4 days are usually the worst. Unless they are very large or deep, they usually heal without scarring.

If your child develops canker sores that last longer than 2 weeks or is unable to eat or drink because of the pain, contact your doctor. Also call the doctor if the sores appear more than two or three times a year.


Tests are usually not done to diagnose canker sores, as a doctor can identify them based on medical history and physical exam alone.

If your child has very frequent or severe bouts of recurrent canker sores, the doctor may want to perform tests to look for possible nutritional deficiencies (which can be corrected with dietary changes or using prescription vitamin supplements), immune system deficiencies, and food or other allergies.


Most canker sores will heal on their own in a few days to a couple of weeks. If your child complains of pain during this time, offer over-the-counter pain relievers like ibuprofen or acetaminophen.

If a sore does not get better after a few weeks or keeps coming back, see a doctor or dentist. He or she may prescribe a topical medicine, special mouthwash, or home remedy to help heal the sores.

For medications that are applied directly to the sore, first blot the area dry with a tissue. Use a cotton swab to apply a small amount of the medication, and make sure your child doesn’t eat or drink for at least 30 minutes to make sure that the medicine is not washed away.

Caring for Your Child

Help make canker sores less painful and prevent them from recurring by encouraging your child to:

  • avoid eating abrasive foods, such as potato chips and nuts, which can irritate gums and other delicate mouth tissues
  • try brushing and rinsing with toothpastes and mouthwashes that do not contain SLS
  • use only soft-bristle toothbrushes and be careful not to brush too hard
  • avoid any foods he or she is allergic to
  • avoid spicy, salty, and acidic foods (such as lemons and tomatoes), which can aggravate tender mouth sores

Although they can certainly be a pain, in most cases, canker sores aren’t a huge problem. Many people have learned to deal with them — and your child can, too.

Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: January 2013