Kraft M, Hofmeier KS, Ruëff F, et al. - Since there exists little knowledge regarding the causes of biphasic anaphylaxis, researchers used data from the Anaphylaxis Registry (from 11 countries) to define factors predisposing for biphasic anaphylaxis in order to acquire a better understanding of these reactions. They analyzed 8,736 patients with monophasic and 435 biphasic anaphylaxis. The rate of biphasic reactions was estimated to be 4.7%. The risk factors identified were: reaction severity; multiorgan involvement; skin, gastrointestinal, severe respiratory, and cardiac symptoms; anaphylaxis due to peanut/tree nut or an unknown elicitor; exercise as a cofactor; chronic urticaria as a comorbidity; a prolonged interval between the contact with the elicitor and start of primary symptoms; and antihistamine therapy. More often, severely affected patients with multiorgan involvement had a biphasic course of anaphylaxis. However, multiple additional predictors were unveiled, indicating a more complex pathogenesis of biphasic reactions than being a rebound of a severe primary reaction.