Canker sores are sometimes thought to be caused by HSV, but this is not true. Canker sores occur only inside the mouth, on the tongue, and on the soft palate (roof of mouth), not on skin surfaces. Although they reoccur, they are not contagious, usually are self-limiting, and have almost no complications. Canker sores are caused by substances that irritate the lining of the mouth.
^ Nasser M, Fedorowicz Z, Khoshnevisan MH, Shahiri Tabarestani M (October 2008). "Acyclovir for treating primary herpetic gingivostomatitis". The Cochrane Database of Systematic Reviews (4): CD006700. doi:10.1002/14651858.CD006700.pub2. PMID 18843726. (Retracted, see doi:10.1002/14651858.cd006700.pub3. If this is an intentional citation to a retracted paper, please replace {{Retracted}} with {{Retracted|intentional=yes}}.)

Oral herpes (HSV-1) infection (or exposure without noticeable infection) is common. About 65% of the U.S. population has detectable antibodies to HSV-1 by age 40. This article will focus on HSV-1, or oral herpes, not on HSV-2, also commonly known as genital herpes. Genital herpes is considered to be a sexually transmitted disease (STD). In addition, HSV-2 virus should not be confused with human papillomavirus (HPV), the cause of genital warts, and some cervical and other cancer types.
There’s herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). “HSV-1 and HSV-2 are different but closely related viruses,” says Dr. Christine Johnston, MPH, who is the Associate Medical Director of the Virology Research Clinic at the University of Washington. Johnston explains that both are transmitted through close mucosal or skin contact with infected secretions. HSV-1 primarily causes oral outbreaks, also known as cold sores, and HSV-2 usually causes genital outbreaks. But HSV-1 can also cause genital outbreaks through oral-to-genital contact, according to the CDC. According to Johnston, genital HSV-1 is less likely to recur than HSV-2, and there’s less asymptomatic shedding (transmitting the virus without realizing it) with HSV-1 than with HSV-2.
To reduce the chance of acquiring HSV-1, avoid touching saliva, skin, or mucous membranes of people who have HSV-1 lesions. Prevention of genital HSV may be accomplished by latex condoms, but protection is never 100%. Spermicides do not protect against HSV. Some clinicians recommend using dental dams (small latex squares) during oral sex, but like condoms, they are not 100% protective.
"When you are having an outbreak of oral herpes, symptoms usually start with a burning, itching or tingling sensation on your lips," Michael says. "This will intensify until a small rash, and then blisters, appear. These sores are commonly called 'cold sores'. The blisters are usually filled with a clear or slightly yellow liquid. Over a short time, these blisters will burst leaving a painful, raw area. These will then dry and scab over. The scabs will generally fall off after a week or two, leaving fresh clear skin beneath."
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