 Reactive oxygen species, ROS, such as superoxide (O2–), hydrogen peroxide (H2O2), hydroxyl radicals (HO•), and singlet oxygen (1O2), can also produce DSBs as a result of ionizing radiation as well as cellular metabolic processes that are naturally occurring.DSBs can also be caused by the action of DNA polymerase while attempting to replicate DNA over a nick that was introduced as a result of DNA damage.There are many types of DNA damage, but DSBs, in particular, are the most harmful as both strands are completely disjointed from the rest of the chromosome.