Reactive oxygen species (ROS), byproducts of oxygen metabolism, are present in the cells as a consequence of living in an oxygen-rich atmosphere. ROS can be generated by both endogenous and exogenous sources, such as mitochondria and carcinogens, respectively.

ROS contain superoxide (O2•−) and hydrogen peroxide (H2O2), and are important for the normal function of many cellular processes, including metabolism, cell growth and differentiation, immune responses and apoptosis.

Low levels of ROS serve as secondary messengers and are essential for carrying out these cellular functions.

Overproduction of ROS and generation of highly reactive ROS, for example hydroxyl (•OH) radicals, can attack lipids, protein, DNA, and other cellular components, leading to numerous diseases, among them cancer, and cardiovascular and neurological disorders.

In humans, oxidative stress is thought to be involved in the development of Asperger syndrome,^[2]ADHD,^[3]cancer,^[4]Parkinson’s disease,^[5]Lafora disease,^[6]