The cause of fever blisters is a strain of the herpes simplex virus. The virus is highly contagious and affects up to 80 percent of children and adults in the United States, according to the National Institute of Dental and Craniofacial Research. Other common names for fever blisters are oral herpes and cold sores.
There are two types of the herpes simplex virus. Herpes simplex virus type 1 (HSV1) is the type that normally causes oral herpes, which is characterized by fever blisters. Herpes simplex virus type 2 (HSV2) is the strain that usually causes genital herpes. However, under certain conditions, HSV2 can also cause fever blisters.
The herpes virus enters the body through tiny breaks in the skin. It is transmitted through skin-to-skin contact with someone who is already infected with the virus. Once inside the body, the virus usually lies dormant for long periods, awakening every so often. When the virus awakens and becomes active, it causes an outbreak of blisters on and around the mouth that lasts for approximately two weeks. When fever blisters are present, the virus is highly contagious.
Many people have recurring episodes of fever blister outbreaks. Although it isn’t fully understood why some people infected with herpes have recurring outbreaks and others do not, certain factors seem to be related. The most common include emotional stress, illness, injury, fever and exposure to sunlight. In general, anything that weakens the immune system makes a person more susceptible to outbreaks.
The most common method of transmitting the herpes virus type 1 is by kissing, but it can also be spread by mouth-to-genital contact, as in oral sex. Children typically get the virus when kissed by an infected adult who is a relative or close friend. Children often transmit the virus by rubbing their fever blisters and then touching other children.
There is no known cure for fever blisters. Once the herpes virus enters the body, it stays there. There are, however, measures you can take to help protect yourself against infection. The Mayo Clinic recommends that you avoid kissing and skin-to-skin contact with an infected person when blisters are present, and avoid sharing personal items, such as razors, lip balm and towels. You should also use sunblock on the face and lips and try to avoid known triggers.
Fever blisters are often confused with canker sores. According to the Mayo Clinic, they are quite different. Canker sores, which are not contagious, are ulcers that occur inside the mouth, on the tongue and on the inner lining of the cheeks and lips. Fever blisters normally appear on the outside of the mouth, lips and surrounding area.