Tooth whitening is the process of lightening the shade of teeth. Whitening process may involve changing the intrinsic color of the tooth or removing the external stains on the teeth. What are bleaching agents and how do they work? Basically bleaching agents are either carbamide peroxide (10 to 44% concentration) or hydrogen peroxide (3 to 16% concentration). When Hydrogen peroxide reaches the tooth surface it penetrates inside where it acts as an oxidizing agent and breaks down into unstable free radicals. These free radicals bind to Organic pigmented molecules there by converting them into small less pigmented components.