Acts as an endoplasmic reticulum (ER) thiol peroxidase that maintains ER redox homeostasis and supports oxidative protein folding (PubMed:32719007). Rapidly reacts with hydrogen peroxide to form sulfenylated/disulfide intermediates and oxidizes protein disulfide isomerase (PDI) family members, promoting disulfide-bond formation (PubMed:21215271). Functions in a redox relay with ERO1A, using ERO1A- generated H(2)O(2) to drive PDI oxidation, linking peroxide detoxification to productive disulfide formation (PubMed:23919619). Protects esophageal epithelia from hydrogen peroxide-induced oxidative stress by reducing reactive oxygen species (ROS) and preventing oxidative DNA damage and double-strand breaks (PubMed:22157330). {ECO:0000269|PubMed:21215271, ECO:0000269|PubMed:22157330, ECO:0000269|PubMed:23919619, ECO:0000269|PubMed:32719007}. This is the function of Ensembl gene identifier ENSG00000116157 (GPX7, glutathione peroxidase 7).