We read with great interest the article “Estrogen increases the severity of anaphylaxis in female mice through enhanced endothelial nitric oxide synthase expression and nitric oxide production” by Hox et al.1 Therein, the authors provide experimental evidence that female mice exhibit more severe anaphylactic reactions than do their male counterparts and offer mechanistic insights by showing that estrogen promotes vascular leakage during an anaphylactic event via enhanced nitric oxide production.