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What is a Mouth Sore?

A mouth sore can develop anywhere inside or outside the mouth including the inner cheeks, the bottom of the mouth, the gums, tongue, or the lips.

There are several different forms, but the two most common ones are cold sores - also called fever blisters - and canker sores. If the sore is on the outside of the lips, it is called a cold sore. If it is on the inside of the mouth, it is called a canker sore.

Cold sores, located on the outside of the lips, are caused by the highly contagious herpes simplex 1 virus. They may develop after coming in contact with another person who has a cold sore. If you have a history of cold sores, new cold sores may be triggered by stress, sun exposure, or hormone changes. You may feel tingling, burning, or tenderness before the cold sore appears and develops into a blister.

Canker sores, found inside the mouth, are not contagious and they may be pale white or grey with redness around the edges. In addition, one canker sore or a group of them may develop inside the mouth.

Canker sores may be caused by a weak immune system (from the cold or the flu), hormone changes, stress, or a deficiency of vitamins and minerals. These mouth sores may also develop due to irritation from biting your lip, tongue, or cheek, burning your mouth with hot liquids or food, wearing braces, dentures that fit poorly, a broken or sharp tooth, or chewing tobacco.

Less common causes of mouth sores include illnesses or a reaction to medication like aspirin or chemotherapy.