ROS are natural byproducts of cellular oxidative metabolism, and have significant roles in the modulation of cell death, cell survival, cell signaling, cell differentiation, gene expression, the immune response and inflammation-related factor production. Significant ROS elements include free radicals such as superoxide, hydroxyl, hydrogen peroxide, and carbonate. ROS can act as signaling molecules in intracellular signaling pathways. They are involved in redox signaling, where they modulate the activity of proteins involved in cell signaling cascades. ROS can also influence gene expression through the modulation of transcription factors and epigenetic modifications. They may activate or inhibit certain genes involved in cellular processes such as stress response and growth inflammation. Reactive oxygen species also play a role in the immune response to pathogens, and are generated by neutrophils and macrophages. They assist in eradicating bacteria, parasites and fungi through oxidative damage. Additionally, ROS plays a role in inducing cell proliferation and apoptosis. ROS may act as signaling molecules to stimulate cell proliferation, and excessive amounts of ROS trigger apoptosis pathways, inducing cell death.