Reactive oxygen species (ROS)

Reactive oxygen species are unstable oxygen-containing molecules, such as superoxide and hydrogen peroxide, that readily react with and can damage cell components.

They arise mainly in mitochondria, where a small fraction of the oxygen used to make energy escapes as superoxide, and in immune cells, which generate bursts of them on purpose to kill bacteria. Enzymes convert superoxide to hydrogen peroxide and then to water, and antioxidants such as glutathione and vitamins C and E mop up the rest. At low levels ROS act as signals that regulate growth, adaptation to exercise and immune activation; at high levels they oxidize membranes, proteins and DNA, producing oxidative stress.

Because they last microseconds, ROS are usually measured through the marks they leave, such as lipid peroxidation products or oxidized DNA bases, or with fluorescent probes in cultured cells. The term appears frequently in preclinical CBD studies as a readout of antioxidant activity; a change in ROS in a dish is a mechanistic observation that does not by itself indicate an effect in people or animals.