Health Library

What Are Canker Sores?

Canker sores are small sores that happen inside the cheeks and lips, at the base of the gums, and on or under the tongue. They can make it painful to eat, drink, or even brush teeth.

Canker sores are different from cold sores (fever blisters), which are caused by a virus and found outside the mouth around the lips, on the cheeks or chin, or inside the nostrils. Cold sores are contagious, but canker sores are not.

What Are the Signs & Symptoms of Canker Sores?

Canker sores usually appear as round, painful open sores that have a white or yellowish coating and a red “halo” around them. Most are small (¼ inch, or 6 millimeters across) and shallow, but occasionally can be larger and deeper.

Most often, canker sores pop up alone, but they can appear in small clusters. Sometimes an area will tingle or burn before a canker sore starts to develop.

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.

What Causes Canker Sores?

No one knows exactly what causes canker sores, also known as aphthous (AF-thiss) ulcers. Many things are thought to put a person at risk for them. Diet may play a part. People whose diets are low in folic acid, vitamin B12, and iron seem to develop canker sores more often, as do people with food allergies.

Mouth injuries (like 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 sometimes the sores can be a sign of an immune system problem.

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.

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.

Although canker sores aren’t contagious, the tendency to have outbreaks of canker sores can run in a family.

How Are Canker Sores Diagnosed?

Just because canker sores are fairly common doesn’t mean they should be ignored.

If your child has canker sores that last longer than 2 weeks or can’t eat or drink because of the pain, call your doctor. Also call if the sores appear more than two or three times a year.

Usually, no tests are needed to diagnose canker sores.

If your child gets canker sores a lot or they’re severe, the doctor may want to do tests to look for possible nutrition problems (which can be corrected with dietary changes or prescription vitamin supplements), immune system problems, and food or other allergies.

How Are Canker Sores Treated?

Most canker sores will heal on their own in a few days to a couple of weeks. If they’re painful, you can give your child an over-the-counter pain reliever like ibuprofen or acetaminophen.

If a sore doesn’t get better after a few weeks or sores keeps coming back, see a doctor or dentist. They may prescribe a topical medicine, special mouthwash, or home remedy to help heal the sores.

For medicines 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 medicine, and make sure your child doesn’t eat or drink for at least 30 minutes to make sure it isn’t washed away.

How Can I Help My Child Feel Better?

To help make canker sores less painful and keep them from coming back, encourage 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 don’t contain SLS
• use only soft-bristle toothbrushes and be careful not to brush too hard
• avoid any foods they’re allergic to
• avoid spicy, salty, and acidic foods (such as lemons and tomatoes), which can irritate tender mouth sores