Antioxidants are compounds that inhibit chemical reactions with oxygen. These reactions, which occur in many contexts, include oxidation reactions that cause cell damage in humans and other animals, as well as degradation of fatty foods, resulting in undesirable color changes or rancidity.

The apple burns when left in open air

Oxidation reactions may involve highly reactive molecules called free radicals. Free Radicals are molecules that have lost an electron and try to replace it by reacting with other molecules. This causes the substance to break down. Metals often catalyze reactions with oxygen. This reaction is the formation of rust. Another example would be the half eaten apple. The skinless area quickly oxidizes causing the apple to turn brown. In our bodies, this break down may be a primary cause of Cancer. Antioxidants inhibit these changes by reacting with the free radicals before they can react with oxygen (free radical scavenging) or by reacting with the metals. Naturally occurring antioxidants may also work by interacting directly with oxygen.

Naturally occurring antioxidants include retinoids (vitamin A) and tocopherols (vitamin E), found in many animals and plants; ascorbic acid (vitamin C), found in citrus and other fruits and vegetables; and beta carotene, found in deep orange and dark green vegetables. These may play a significant role in the prevention of cancer, heart disease, immune-deficiency diseases, and aging.

Synthetic antioxidants include butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and propyl gallate. Natural and synthetic antioxidants are added to food to prevent undesirable deterioration. Foods preserved with antioxidants include vegetable oils, bread, and cheese. Antioxidants are also frequently applied to the packaging materials of cereals and nuts.

Although approved by the U.S. Food and Drug Administration, the safety of BHA and BHT is being researched.