[5][6] Dual oxidase is an enzyme that was first identified in the mammalian thyroid gland.

The protein location is not exclusive to thyroid tissue; hDUOX1 is prominent in airway epithelial cells[7] and hDUOX2 in the salivary glands and gastrointestinal tract.

[8][9][10] Investigations into reactive oxygen species (ROS) in biological systems have, until recently, focused on characterization of phagocytic cell processes.

It is now well accepted that production of such species is not restricted to phagocytic cells and can occur in eukaryotic non-phagocytic cell types via NADPH oxidase (NOX) or dual oxidase (DUOX).

Genetic analyses have implicated NOX/DUOX derived ROS in biological roles and pathological conditions including hypertension (NOX1), innate immunity (NOX2/DUOX), otoconia formation in the inner ear (NOX3) and thyroid hormone biosynthesis (DUOX1/2).DUOX2 is the isoform that generates H2O2 utilized by thyroid peroxidase (TPO) for the biosynthesis of thyroid hormones,[11] supported by the discovery of congenital hypothyroidism resultant from an inactivating mutation in the DUOX2 gene.