Free radicals are molecules which contain one or more unpaired electrons. These molecules are highly reactive and tend to initiate chain reactions with other molecules also called oxidants or reactive oxygen particles (ROP). Molecules which protect proteins, lipids, carbohydrates and nucleic acids against free radicals are called antioxidants and so this reaction is called antioxidant defence system. Increased oxidants are antagonized by antioxidants in human body.
In this review, ROP and antioxidant defences will be discussed.