Free radicals and oxidants play a dual role as both toxic and beneficial compounds, since they can be
either harmful or helpful to the body. They are produced either from normal cell metabolisms in situ or
from external sources (pollution, cigarette smoke, radiation, medication). When an overload of free radicals
cannot gradually be destroyed, their accumulation in the body generates a phenomenon called oxidative
stress. This process plays a major part in the development of chronic and degenerative illness such as cancer,
autoimmune disorders, aging, cataract, rheumatoid arthritis, cardiovascular and neurodegenerative
diseases. The human body has several mechanisms to counteract oxidative stress by producing antioxidants,
which are either naturally produced in situ, or externally supplied through foods and/or supplements. This
mini-review deals with the taxonomy, the mechanisms of formation and catabolism of the free radicals, it
examines their beneficial and deleterious effects on cellular activities, it highlights the potential role of the
antioxidants in preventing and repairing damages caused by oxidative stress, and it discusses the antioxidant
supplementation in health maintenance. (Int J Biomed Sci 2008;4(2):89-96)