The process of tooth whitening lightens the colour of a tooth. Tooth whitening can be achieved by either changing the intrinsic colour or by removing and controlling the formation of extrinsic stains. The chemical degradation of the chromogens within or on the tooth is termed as bleaching. Hydrogen peroxide (H2O2) is the active ingredient most commonly used in whitening products and is delivered as either hydrogen peroxide or carbamide peroxide. Hydrogen peroxide is analogous to carbamide peroxide as it is released when the stable complex is in contact with water. When it diffuses into the tooth, hydrogen peroxide acts as an oxidising agent that breaks down to produce unstable free radicals. In the spaces between the inorganic salts in tooth enamel, these unstable free radicals attach to organic pigment molecules resulting in small, less heavily pigmented components. Reflecting less light, these smaller molecules create a "whitening effect". There are different products available on the market to remove stains. For whitening treatment to be successful, dental professionals should correctly diagnose the type, intensity and location of the tooth discolouration. Time exposure and the concentration of the bleaching compound, determines the tooth whitening endpoint.