Jarisch‒Herxheimer reaction.

Syphilis is caused by a spirochete, Treponema pallidum. Diagnosis of syphilis is made with a venereal disease research laboratory test. Treatment of choice is intramuscular injection benzathine Penicillin. The Jarisch‒Herxheimer reaction (JHR) is a transient immunological phenomenon that can occur in patients during treatment for syphilis with penicillin. It is a rare phenomenon but can be a potentially severe one. It manifests clinically with short-term constitutional symptoms such as fever, chills, headache, and myalgia, besides exacerbation of existing cutaneous lesions. We report the case of a 24-year-old man presenting with JHR posttreatment with benzathine penicillin.