Hesperian Health Guides

Canker Sores

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HealthWiki > Where There Is No Dentist > Chapter 7 Part 1: Problems You Will See Most Often > Canker Sores

The exact cause of canker sores is not known. Canker sores affect both adults and children, and are very common among youth. One or more sores can appear at any time. These sores hurt, especially when pieces of food touch them.

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  • A sore can appear on the cheeks, inside the lips, on the tongue, or below the gums on the smooth skin.
  • The sore is white or yellow with the skin around it bright red.
  • The person may have had a similar kind of sore before. It tends to come back.

Note: a sharp edge of a denture rubbing against the gums can make a similar kind of sore.


A canker sore goes away by itself in about 10 days. Medicine does not make that happen any faster. (However, smoothing a denture or fixing a broken tooth does help.) The treatment is simple. Tell the person how to feel more comfortable while waiting for the 10 days to pass:

  • Eat foods that are soft and not likely to hurt the sore.
  • Do not eat spicy food.
  • Drink lots of water.
  • Chew food on the other side of the mouth, away from the sore.

A denture which does not fit should be remade.

In the meantime, leave the denture out of the mouth for 2 or 3 days.

Ask the person to rinse with warm salt water, 4 cups each day until the sore is better.
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If the sore continues after 10 days, it may be infected. Give penicillin.

A sore that does not heal after antibiotic treatment may be cancer. See a doctor immediately.

This page was updated:19 Feb 2018