text: hydrogen peroxide? does anyone know why hydrogen perooxide is harmful to the cell and does anyone have a link that has a list of chemical properties of catalase? thnx peroxidase and catalase are different but they preform the same reaction - they both break down hydrogen peroxide. our bodies don't have peroxidase because it breaks down hydrogen peroxide.peroxide is produced as a harmful byproduct of respiration. the body needs to break down peroxide because it is a powerful oxidizer and acts as a free radical. if peroxide builds up in the body, cellular damage may happen.