©2018 WebMD, Inc. All rights reserved. eMedicineHealth does not provide medical advice, diagnosis or treatment. See Additional Information.

Viral Skin Diseases

Picture of Cold Sores (Fever Blisters)

Picture of Cold Sores (Fever Blisters)

Cold sores are fluid-filled blisters or ulcers that form on the lips and around the mouth. They are caused by the herpes simplex virus (HSV).These viruses also cause genital herpes. Typically, a strain of the virus known as HSV-1 causes cold sores, while HSV-2 causes genital herpes, but both viruses are able to cause cold sores and genital blisters. Another name for cold sores is fever blisters. The herpes viruses that cause cold sores are very contagious. The virus is transmitted by kissing, sharing utensils, and similar activities. Once a person harbors HSV, the virus may periodically reactivate and cause outbreaks. Cold sores start as blisters and eventually burst and ooze before crusting over and healing. An outbreak of cold sores may last anywhere from several days up to 2 weeks.

Image: Courtesy of Dr. Herrmann/ Centers for Disease Control and Prevention (CDC)

Text Reference: "Cold Sores." American Dental Association.