Fever blisters are an extremely common condition of the mouth. Also known as cold sores
(and known medically as herpes labialis), these blisters are the result of being infected with a herpes simplex virus.
Despite its two common names (fever blister and cold sore), you do not need a cold or fever to get the condition.
(Click Causes of Fever Blisters to learn more about the different types of herpes simplex viruses and how they can cause fever blisters.)
Fever Blisters Versus Canker Sores
Many times, fever blisters are confused with another common mouth condition known as canker sores. Both can cause small sores in or around the mouth. Canker sores, however, occur only inside the mouth -- on the tongue and the inside linings of the cheeks, lips, and throat.
Fever blisters, on the other hand, usually occur outside the mouth -- on the lips, chin, cheeks, or in the nostrils. When they do occur inside the mouth, they are usually on the gums or the roof of the mouth. Inside the mouth, fever blisters are smaller than canker sores, heal more quickly, and often begin as a blister.