IGHE and response to penicillin: Regarding the challenges with penicillin in patients with a previous but not present positive s-IgE, a negative sIgE was not associated with tolerance in 63.6% of the tested patients and even a tolerated readministration of penicillins (also during iatrogenic diagnostic workup) may lead to boostering of sIgE with unknown significance, but possibly reoccurrence of penicillin allergy. Further the more indistinct outcomes in the patients with negative challenge but positive post-challenge s-IgE, no firm conclusion can be drawn without challenging the patients once again.