The Herpes 1 and 2 IgG test measures immunoglobulin G, which is a type of long lasting antibody your immune system creates after exposure to herpes simplex virus. Herpes simplex virus type 1 usually affects the mouth and face, while type 2 more commonly affects the genitals. Both viruses can infect either area. IgG antibodies develop slowly during the first weeks after exposure and then remain in the bloodstream for life. This means the presence of IgG usually indicates a past infection rather than a brand new one.
Your immune system produces IgG as part of its adaptive response. Adaptive immunity refers to the branch of the immune system that learns to recognize specific germs and then remembers them for future protection. Once IgG appears, it stays fairly stable over time. Levels do not reliably show how long you have had the virus or how active it is in your body. People without any symptoms can still have detectable IgG. The presence of IgG identifies which herpes type you have been exposed to, which helps guide counseling about transmission risk and symptom management.
A negative IgG result usually means you have not been exposed, although very early infection can produce a false negative because IgG takes time to develop. This early timeframe is called the window period. False positives can also occur, especially with tests that have difficulty distinguishing type 1 from type 2. More advanced assays with better type specific accuracy help reduce this issue. IgM testing is sometimes offered, but it is not considered reliable for diagnosing new infection because IgM can rise during recurrent episodes or cross react with other viruses.
The most useful aspects of an IgG result are understanding which virus type is present, clarifying why certain symptoms may be occurring, and learning how to reduce transmission to partners. People with type 2 IgG usually have a higher risk of genital outbreaks, although many remain completely symptom free. Suppressive antiviral therapy can lower both outbreaks and transmission risk even when IgG levels remain unchanged.
