Still, condoms should unquestionably be a part of your arsenal in protecting yourself from a herpes genital infection. Although the amount of protection from simply using a condom will be less than for a disease like HIV that can be prevented by blocking secretions, that doesn't mean the reduction is insignificant. A 2009 meta-analysis of six pre-existing studies -- that all peripherally addressed the question of how condoms affect herpes transmission -- found that consistent condom users saw a 30 percent reduction in their risk of getting herpes from their partners. However, condom use has to be consistent. The study also found that every unprotected sex act increased the risk of herpes transmission.
There are other ways of reducing the risk of herpes transmission including suppressive therapy to reduce both symptoms and the amount of viral shedding and not having sex during or right before an outbreak; however, condoms should also play an important role in reducing the spread of the herpes virus. For maximum benefit, you should use them or other barriers every time you have sex, since herpes can be spread even when a person has no symptoms. Barriers should also be used for oral sex, since genital herpes can be spread to the mouth and cold sores can also infect the genitals.
Martin, E.T. et al (2009) "A Pooled Analysis of the Effect of Condoms in Preventing HSV-2 Acquisition" Arch Intern Med. 169(13):1233-1240