Oxidative stress describes a state of physiological stress in the body that arises from exposure to high levels of reactive oxygen species (ROS) relative to the level of neutralizing antioxidants.

Free radicals can interact with molecules in the body and damage various cell components such as DNA, protein and lipids, giving rise to various disease states.

Much of the damage caused by oxidative stress arises from its modification of the DNA inside a cell's nucleus which gives rise to mutations.Reduction or redox potential refers to a substance's ability to gain or lose an electron. A strong reducing agent for a example will have a high-electron transfer potential. When the presence of free radicals causes only a small change in the redox potential of a cell, the cell's antioxidant system is stimulated and protects the body from the damage caused by free radicals. In more severe cases, however, a cell can become necrotic and die.

Examples of the conditions caused by free radical damage include:

• Neurodegenerative disorders such as Parkinson's disease, multiple sclerosis and Alzheimer's disease
• Mutagenesis and cancer
• Heart and blood vessel disorders such as heart failure, heart attacks, atherosclerosis and cardiac ischemia
• Lung conditions such as emphysema and lung cancer
• Chronic fatigue syndrome
• Cataracts and vision disorders such as retrolental fibroplasia
• Arthritis and inflammatory disease
• Diabetes
• Kidney disease
• Pancreatitis
• Gut disorders such as inflammatory bowel disease
• Skin lesions such as those caused by sun damage
• Lipoprotein oxidation in newborns
• Failure of organ transplant
• Frostbite
• Hemolytic anemia, protoporphyrin, photooxidation
• Autoimmune diseases