Biological oxidation is the basis of all life processes. Active forms of oxygen called radicals are produced during the breathing process and consequently the amount of atmospheric O2 within our cells. This shows that, in our lifetime, the production of free radicals is a normal feature of our basic functions. They are able to attack (oxidise) any biological substrate. Because of the above, enzymatic antioxidant systems have phylogenetically developed inside our cells, such as: Catalase, Dismutase, Peroxidase etc., and non-enzymatic systems represented by vitamins: A, C, E, B, the efficiency of which is of fundamental importance for our lives.

It is essential to consider that at a molecular level, the R.L. attack all four groups of biomolecules which take part in our physiological processes such as: Carbohydrates, Lipids, Proteins, and Nucleic Acids.

Flavonoids, ubiquinones, quercetines and tocochinons are all important redox systems. The redox cycles can be started and sustained by non-enzymatic electron carriers, such as ascorbic acid or reduced glutathione, or enzymatic carriers such as flavins, which terminate the chain of radical reactions. We know that oxidative damage produced by radicals to the body cannot be repaired or prevented by any one vitamin, as it is also true that there is not one single redox system to defend ourselves. Moreover, a reserve of both of the above would be exhausted in a few seconds or minutes if there is no possibility of regeneration. The regeneration of the redox system is called redox coupling. The first signs of aging appear in organs which are rich in fundamental substances, such as skin, that shows a marked increase in lines on the face and body, with degeneration of collagen and elastic fibres.

A high level of R.L. in tissues and/or in biological fluids can be caused by excessive production of the same or by a reduced antioxidant capacity. In both cases it could determine a health disorder or simply an epiphenomenon episode. This ambiguity is still today the subject of considerable scientific discussion. Although some parameters are now accepted as a standard used to determine the oxidation state of our cells.