Reactive oxygen and nitrogen species (ROS/RNS) are highly reactive molecules that can damage cells. They include radicals like superoxide and hydroxyl, as well as non-radical species like hydrogen peroxide. ROS/RNS are produced through normal cellular processes but also from external sources like radiation and pollutants. They can cause oxidative damage to lipids, proteins, and DNA if not neutralized by antioxidant defenses. This oxidative stress has been linked to many diseases due to disruption of redox signaling and control in the cell.