Reactive Oxygen Species

Reactive oxygen species (ROS) are chemically reactive molecules derived from molecular oxygen — including superoxide (O2•−), hydrogen peroxide (H2O2), and hydroxyl radical (•OH) — produced as byproducts of oxidative metabolism in mitochondria and other cellular compartments. At low concentrations, ROS function as signaling molecules that regulate cell proliferation, stress response, and apoptosis. At high concentrations, they oxidize proteins, lipids, and DNA, contributing to mutational load, cellular aging, and disease — a phenomenon collectively called oxidative stress. The ambiguity of ROS as both signal and toxin has made "antioxidants are good" a persistent oversimplification: suppressing ROS signaling disrupts immune function and cellular housekeeping. Whether oxidative stress is primarily a cause of aging or a consequence of other processes remains contested in evolutionary gerontology.