Oxidative stress is a shift in the balance within cellular oxidation - reduction reactions towards oxidation, during which it creates excessive free radicals and a loss in balance in their creation and destruction. The results of the oxidative stress are increased oxidation, increased production of oxidation products, a reduction of antioxidant protection and failure to repair oxidative damage, which in turn leads to the damage or death of cells, death specific molecules or even the whole organism. The free radical is a neutral or charged chemical species that has at least one unpaired electron in the outer shell. Reactive oxygen compounds and reactive nitrogen compounds are the most common causes of oxidative stress. Oxidative stress doesn’t always have a negative effect . There are certain known positive effects of oxidative stress , such as "respiratory burst”. Antioxidant defense is based precisely on the prevention of their occurrence and their removal by the enzyme, as well as the repair of damage caused and the removal of damaged molecules. Antioxidants react with the free radicals, stabilizing them and deactivating them, thus protecting the body against oxidative stress and preventing cell damage. The antioxidant "catchers" of free radicals are different vitamins (A, E, C, beta-carotene), minerals (selenium), enzymes (superoxide dismutase, glutathione peroxidase , catalase), estrogens, bioflavonoids, melatonin, serotonin, ubiquinon and many others that are being researched.