Causes and Symptoms of Canker Sores

May 7th 2016

If your canker sore is accompanied by pain, a rash, diarrhea or a fever, see a doctor to find out what's going on. You should also seek medical advice if a canker sore lasts three weeks or more.

Causes of Canker Sores

While the exact mechanism behind canker sores isn't known as of 2015, their appearance is often related to stress. Some scientists believe that canker sores develop as an overreaction to Streptococcus bacteria, based on the fact that Streptococcus is often found in a canker sore. Citrus and other acidic foods regularly trigger the appearance of a canker sore and irritate it. Mouth injuries caused at the dentist's office, teeth brushing or dental braces can also cause canker sores. Women frequently develop canker sores around the time of their menstrual periods, and hormonal fluctuations may play a role in their appearance. The body's immune system may also play a part in the development of canker sores. People with allergies seem to be more prone to them. In addition, nutritional deficiencies of vitamin B12, iron, folic acid or zinc can lead to canker sores.

Symptoms of Canker Sores

Canker sores appear in the mouth as small, white or yellow blisters. The sores are usually 1 to 2 millimeters in diameter and are often surrounded by a ring of red tissue. Smaller sores sometimes appear in clusters. Before the ulcer erupts, the area around it typically feels tender and painful, with the pain often accompanied by a tingling feeling that sometimes lasts for up to 24 hours. Typically a canker sore is diagnosed just based on its appearance. However, if the breakout is severe or if your physician believes the sore is caused by a hormonal or immune system disorder, he may do some blood tests. Mouth cancers initially may look like canker sores, but they do not heal on their own as canker sores do.

Treatment of Canker Sores

While canker sores usually heal on their own given time, you can treat them with over-the-counter corticosteroid ointments or antimicrobial mouth rinses. A doctor or dentist may also prescribe painkillers. Stay away from citrus and spicy or hot foods, which are likely to exacerbate the pain.


Canker sores are small, painful ulcers that find a home in the mouth. They typically appear on the inside of the lip or cheek, and they can make eating and talking difficult and even painful. While small canker sores typically disappear within a couple of weeks with no after-effects, the rarer large variety can take many weeks to heal and may leave scars. Canker sores, unlike cold sores, are not contagious.

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