In the case of nut-induced anaphylaxis, as with other foods, symptoms typically present within 5–30 minutes of ingestion.20 Biphasic reactions, in which return of anaphylactic symptoms occurs following an asymptomatic period of an hour or more after the initial reaction, without further exposure to antigen, can occur in 3%–20% of severe food reactions.9,21,22 However, the mechanism of biphasic anaphylaxis is largely unknown, and these late phase reactions have been observed in only 2% of anaphylaxis induced by foods during inpatient oral food challenges (OFCs).23 Biphasic reactions typically develop within 8 hours of resolution of the initial reaction, but may occur up to 72 hours later.24 Risk factors for late phase reactions may include delayed onset of initial symptoms (>30 minutes), β-blockade, administration delay or inadequate dose of epinephrine, as well as reaction to an ingested allergen (food), as opposed to an injected allergen.22