Free radicals and other reactive oxygen species are derived either from normal essential metabolic processes in the human body or from external sources such as exposure to x-rays ozone cigarette smoking air pollutants and industrial chemicals
Free radical formation occurs continuously in the cells as a consequence of both enzymatic and non-enzymatic reaction
Serve as sources of free radicals include those involved in the respiratory chin in phagocytosis in prostaglandin synthesis and in the cytochrome p450 system . free radicals also arise in non-enzymatic reactions of oxygen with organic compounds as well as those initiated by ionizing radiations. Some internally generated sources of free radicals