How can I tell if I really have an allergic reaction, and not a variant of the herpes virus? I have had a sore throat for a few days, and began breaking out with chickenpox like symptoms, with blisters starting on my scalp, spreading all over to my face,

This . This definitely sounds like it could have been a herpes outbreak as opposed to an allergic reaction. There are two types of herpes viruses (1 and 2). In the past type 1 was associated with cold sores and type 2 with genital herpes. Now it has been proven that both types can be found in either location. A quick way for you to know if you have been exposed to the herpes virus is by requesting a blood tests that checks for antibodies to both types of herpes. If the test comes back positive for either type then you can assume that you may have had an outbreak, and it if happens again see your doctor at the onset of symptoms and request treatment for herpes. Best of luck.