These mechanisms are divided into:

• Endogenous antioxidants, such as cellular enzymes: superoxide dismutase(SOD), catalase and glutathione peroxidase
• Exogenous antioxidants, such as A, C and E vitamins acquired by diet or pharmacological supplements.

Antioxidants donate electrons to free radicals without themselves becoming harmful substances for the body.

Out of all oxidizing species, hydroxyl radical ^•OH is the strongest. Mammals have a lack of endogenous detoxification systems to neutralize it. Thus, the therapeutic objective of neutralizing the ^•OH becomes critical to improve the oxidative damage.

Diverse substances are considered hydroxyl radical scavengers and many exogenous antioxidants have shown their capability to reduce ROS levels in oxidative stress related diseases. Nevertheless, research suggests that excessive antioxidant treatment is not beneficial and even may be harmful because it decreases levels of critical ROS such as ^•O₂- y H₂O₂. This ROS play a key role in cell functions and they regulate processes such as cell proliferation and differentiation.

Consequently, to decrease oxidative state intensively may provoke undesired side effects by interfering with these essential defense mechanisms.

Unlike other antioxidants that eliminate both harmful and beneficial ROS, hydrogen has the capability to selectively scavenge harmful ROS without interfering with beneficial ROS which cooperate with immunity and biological activity.