If you're like many people, you've probably - at one time or another - had a cold sore or canker sore. Both types of sores are unpleasant: they can be painful and interfere with socializing and your enjoyment of meals.

Both canker and cold sores are common and the two are often confused. To distinguish between them, remember that canker sores occur inside the mouth and cold sores usually occur outside the mouth. Their appearance also differs.

Canker Sores

Canker sores occur inside the mouth. There may be one or a number of small ulcers with a white or gray base and red border. Some experts think that they may be caused by bacteria or viruses or a problem with the immune system.

Canker sores are more likely to occur when people are fatigued, under stress or have allergies. Cuts, reactions to hot or cold foods or drinks may also contribute to canker sores.

Although canker sores usually heal after a week or two, temporary relief can be obtained from antimicrobial mouthrinses or topical anesthetics. Canker sores can be irratated by hot, spicy or acidic foods. Recurrent outbreaks are common.

Cold Sores

Cold sores, also known as fever blister or herpes simplex, are fluid-filled blisters that form around the lips and sometimes under the nose and around the chin. They may also erupt inside the mouth. Cold sores are very contagious.

Cold sores are usually caused by herpes virus type 1. Once infected, the virus usually stays in the body, often causing recurrent attacks. These attacks may follow a fever, sunburn, skin irritation or emotional upset. The virus remains inactive for some people, however.

Cold sores usually heal in about a week. Temporary relief can be provided by over-the-counter topical anesthetics. Prescription antiviral drugs may reduce these kinds of viral infections.

Any mouth sore that persists for a week should be examined by your dentist. Sometimes a biopsy (tissue sample taken for testing) is necessary to determine the cause of some mouth sores and rule out cancer.