HSV-1 and -2 are transmitted from contact with an infectious area of the skin during reactivations of the virus. Although less likely, the herpes viruses can be transmitted during latency. Transmission is likely to occur during symptomatic reactivation of the virus that causes visible and typical skin sores. Asymptomatic reactivation means that the virus causes atypical, subtle or hard to notice symptoms that are not identified as an active herpes infection. Atypical symptoms are often attributed to other causes such as a yeast infection. HSV-1 is usually acquired orally during childhood, but may also be sexually transmitted. HSV-2 is primarily a sexually transmitted infection but rates of HSV-1 genital infections are increasing.
Both viruses may also be transmitted vertically during childbirth, although the real risk is very low. The risk of infection is minimal if the mother has no symptoms or exposed blisters during delivery. The risk is considerable when the mother gets the virus for the first time during late pregnancy.
Symptoms resulting from primary infection with HSV are usually much more severe than subsequent outbreaks, as the body has not had a chance to produce antibodies. This first outbreak of oral herpes (cold sores) carries a low (≈1%) risk of developing aseptic meningitis.