What Are Cold Sores?

In the mirror this morning, you may have faced the unwelcome but familiar sight of small, fluid-filled blisters around or in your mouth. Often called fever blisters or cold sores, they are the mark of a common and highly contagious viral disease—oral herpes.

While many people think of herpes as a sexually transmitted disease, the virus that causes cold sores is a different strain of the one that causes genital herpes. The oral herpes virus is also related to the viruses that cause infectious mononucleosis, chicken pox, and shingles.

Canker Sores Are Not Cold Sores
If a canker sore appears inside your mouth, you may find it difficult to distinguish it from a cold sore. Canker sores are not caused by the oral herpes virus, and the treatment is different. Canker sores—tiny, shallow ulcers that cause mouth pain for about five to 10 days—usually occur on the tongue or inside the lips or cheeks. Research suggests that canker sores develop as a response to a localized trauma or irritation. Unlike cold sores, canker sores are not contagious and may be treated with a steroid ointment.