reactive oxygen species

Definition of reactive oxygen species
National Cancer Institute

reactive oxygen species

(ree-AK-tive OK-sih-jen SPEE-sees)
A type of unstable molecule that contains oxygen and that easily reacts with other molecules in a cell. A build up of reactive oxygen species in cells may cause damage to DNA, RNA, and proteins, and may cause cell death. Reactive oxygen species are free radicals. Also called oxygen radical.

Source: NCI Dictionary of Cancer Terms