Anaphylactoid reactions or pseudoallergic reactions are immediate systemic reactions that mimic anaphylaxis but are caused by non-IgE-mediated release of mediators from mast cells and basophils.3 Anaphylactoid reactions may occur with the first exposure to an antigen and may be clinically indistinguishable from anaphylaxis. This evidence concerns the gene IGHE and anaphylaxis.