EPHX1 is a human gene that encodes microsomal epoxide hydrolase, a phase I/II detoxification enzyme located in the endoplasmic reticulum. Biochemically it belongs to the epoxide hydrolase family and acts on small epoxide substrates formed from xenobiotics and endogenous lipids. Variants in EPHX1 were identified in genetic screens focused on metabolic enzymes and have been studied for their influence on individual differences in xenobiotic handling. The core function of EPHX1 is to catalyze hydrolysis of epoxide groups to vicinal diols, reducing the reactivity of epoxide intermediates generated by cytochrome P450 metabolism or by oxidative stress. That activity links EPHX1 to broader detox pathways, interacting functionally with cytochrome enzymes, glutathione-related systems, and other phase II processes that together determine how quickly and safely the body processes many environmental chemicals.

Variants associated with relatively higher EPHX1 activity suggest faster conversion of reactive epoxides into less-reactive diols, which can change the mix and persistence of metabolites after exposure. Variants associated with relatively lower activity suggest slower conversion and potentially longer persistence of reactive intermediates. These patterns are associations that gain clinical meaning only when read alongside measured toxicant levels, other detoxification genotypes, and exposure history provided by the full Toxin Zoomer panel.

EPHX1 is included in the Toxin Zoomer because it evaluates a key enzymatic step in processing epoxide intermediates from chemicals, metals, and lipid oxidation. Knowing EPHX1 variant status helps clinicians interpret urinary toxicant profiles and other detox genes to better characterize individual detox capacity and exposure sensitivity for personalized, exposure‑aligned care.