In the June 2008 edition of "Archives of Internal Medicine,"internist Christina Cernik, M.D., explains that cold sores are a common complaint encounted by primary care physicians. Ninety percent of cold sores develop on the lips, according to Cernik, with the remainder divided evenly between surfaces inside the mouth and surfaces elsewhere on the face. All cold sores share a common cause: one of two types of the herpes simplex virus.
Virus Characteristics
There are two types of herpes simplex viruses, herpes simplex-1 and herpes simplex-2. Although doctors have traditionally associated cold sores with herpes simplex-1 and genital herpes with herpes simplex-2, in the 2008 edition of "Harrison's Principles of Internal Medicine," University of Washington Professor of Medicine Lawrence Corey, M.D. notes that each type of the virus can produce both cold sores and genital herpes. Although, according to Corey, the viruses share only 50 percent of the same genes, they produce identical symptoms. While herpes simplex-1 accounts for most cases of cold sores, only laboratory tests can effectively distinguish between the two.
Virus Prevalence
The American Social Health Association estimates that 50 to 80 percent of the population has been exposed to the herpes simplex-1 virus, compared to about 20 percent for the herpes simplex-2 virus. Since infection with one type of the virus does not confer immunity against the other, a small number of people have both. Prevalence increases through life, with up to 90 percent of individuals over 50 testing positive for exposure. Most people contract the herpes simplex-1 virus as children, when they receive kisses from infected friends or family members or though the sharing of objects such as eating utensils and toys. The prevalence of herpes simplex-2 virus infections begins to increase in adolescence, correlating with the onset of sexual activity.
Virus Triggers
Doctors believe that the immune system does not completely clear herpes simplex viruses. Instead, according to the National Institute of Dental and Craniofacial Research, the viruses hide out in clusters of nerve cells called "ganglia." While the viruses mostly remain inactive, they periodically reactivate in response to triggers. As a result, the National Institute of Dental and Craniofacial Research estimates, about 20 to 40 percent of people experience periodic recurrences of cold sores. Triggers may be internal or external. Common internal triggers include stress, fatigue, menstruation, pregnancy and illnesses such as a cold or the flu, or more serious conditions such as AIDS or cancer. Common external triggers include dental care, injuries to the mouth, food allergies and sunlight or ultraviolet lamps.
References
- "Archives of Internal Medicine"; "The Treatment of Herpes Simplex Infections; Christina Cernik, M.D., et al.; June 9, 2008
- "Harrison's Principles of Internal Medicine, 23rd Edition"; Anthony S. Fauci, M.D. et al.; 2008
- National Institute of Dental and Craniofacial Research: Oral Health in America: A Report of the Surgeon General
- Academy of General Dentistry: What Are Cold Sores?
