The Free Radical Threat During the normal metabolism of cells, oxidation reactions produce harmful byproducts known as free radicals. These highly reactive molecules react with DNA, protein and other cellular components, causing a great deal of damage. In the process, they produce more free radicals in a chain reaction. Antioxidants are compounds that are able to quench free radicals and stop them from causing cellular damage. However, most antioxidants become mild free radicals themselves in this process, which, in the long term can cause harm if not dealt with.