Transmission of HSV-1
HSV-1 is the herpes virus that, for the most part, causes cold sores. However, your partner can transmit this virus from her mouth to your genitals, and can sometimes trigger a genital herpes infection.
Transmission of HSV-2
Most cases of genital herpes are triggered by the HSV-2 virus, which can be transmitted through oral, vaginal and anal sex. People who are having an active outbreak should refrain from sexual activity.
Herpes causes sores on the genitals or in the mouth that occur in outbreaks (sores appear and go away), which become less frequent with time. The CDC reports that HSV-2 also can cause fever and swollen glands, although most people with HSV-2 never develop symptoms.
Even in the absence of an outbreak, it is possible to transmit HSV-2 to your partner. You should use barriers like condoms, female condoms and dental dams, which can reduce your chances of contracting HSV-2. However, be aware that herpes can be spread through skin that is not covered by a barrier.
The CDC reports that daily medication treatment for herpes helps reduce the risk of transmitting herpes to sexual partners.
There are a very limited number of cases of nonsexual transmission of herpes, as from sharing a toilet seat or towel. Herpes.org lists the precautions people with herpes should take during out an outbreak to prevent these (see Resources).