Generates hydrogen peroxide (H2O2) which is required for the activity of thyroid peroxidase/TPO and lactoperoxidase/LPO (PubMed:10806195, PubMed:15972824). Plays a role in thyroid hormone synthesis (PubMed:10806195). Also required for lactoperoxidase-mediated antimicrobial defense at the surface of mucosa (PubMed:12824283). Antimicrobial agent hypothiocyanite (OSCN-), which is produced by LPO from DUOX1-derived H2O2, promotes influenza virus inactivation by reducing viral binding to and entry into host cells (PubMed:34168077). Promotes antiviral immunity by increasing airway cytokine levels, promoting innate immune cell recruitment and reducing airway epithelial cell apoptosis (By similarity). In response to bacterial stimuli, activated by ATP and promotes EGFR/ERK signaling, ADAM17 activation, and EGFR ligand shedding, leading to enhanced CXCL8/IL8 expression and secretion in airway epithelia (PubMed:19386603). Synthesizes NAADP from its reduced NAADPH form which promotes Ca(2+) signaling during T cell activation (PubMed:34784249). In addition to its oxidase activity, has also been shown to have peroxidase activity through its N-terminal peroxidase-like domain (PubMed:11514595). However, another study showed that the isolated peroxidase-like domain does not bind heme and has no intrinsic peroxidase activity (PubMed:19460756). {ECO:0000250|UniProtKB:A2AQ92, ECO:0000269|PubMed:10806195, ECO:0000269|PubMed:11514595, ECO:0000269|PubMed:12824283, ECO:0000269|PubMed:15972824, ECO:0000269|PubMed:19386603, ECO:0000269|PubMed:19460756, ECO:0000269|PubMed:34168077, ECO:0000269|PubMed:34784249}. This is the function of ENSG00000137857 (DUOX1, dual oxidase 1).