Free radicals are often very reactive and unstable.
They are common as transient intermediaries in chemical reactions. Processes involving free radicals are used in the production of rubber and plastics, for example, and the radicals are common in chain reactions such as the ones that produce fire. They also occur in body chemistry, in processes such as the destruction of invading organsims by white blood cells. Free radicals might play a role in various maladies, such as arthritis, heart desease, and Alzheimer's disease. When natural enzyme controls fail, free radicals in the body attack lipids, proteins, and nucleic acids.