*7.1.7 Oxidative damage theory*

 Denham Harman proposed free radical theory of aging in 1950s and according to this theory oxygen free radicals formed during normal metabolic process just because of lot of oxidative damage to macromolecules. This theory is further modified and a new theory came in existence that is 'Oxidative Stress Theory of Aging'. According to this theory oxygen species like peroxide and aldehyde are not technically free radicals but they play an important role in oxidative damage to cell. As age passes the imbalance between proxidant and antioxidant leads to an accumulation of oxidative damage in variety of macromolecules and cause failure of normal cellular process and leading to aging [49, 50].
