IgM and IgG refer to different kinds of blood antibodies which your body produces to fight the herpes virus. IgM antibodies start to appear within a few days from exposure to the virus, reach a peak level within two to four weeks and slowly disappear within two to three months. IgM antibodies are not type specific meaning there is no way to know whether the antibodies come from HSV-1 or HSV-2. This is why an IgM test alone is not a good idea since by itself it will not tell you if you have HSV-1 or HSV-2. IgG antibodies on the other hand are type specific. They can be used to determine which type of herpes virus you have. They may appear within three to four weeks and are definitely present four to six months after exposure.