Jarisch-Herxheimer reaction

Jarisch-Herxheimer Reaction occurs when large quantities of toxins are released into the body as bacteria (typically Spirochetal bacteria) die, due to antibiotic treatment. It is important to distinguish this reaction from Penicillin allergy. In the USMLE one is typically given a case with allergic symptoms following treatment of syphilis with Penicillin. There are usually other clues in the question about the diagnosis. Dont blindly mark Jarisch Herxheimer as the answer.