In biological systems, the normal processes of oxidation (plus contributions from ionizing radiation and pro-oxidant chemicals) produce highly reactive free radicals. These can readily react with and damage other molecules, including DNA in cell nuclei or mitochondria. In some cases the body uses free radicals to destroy foreign or unwanted objects, such as in an infection or cancer. However, in the wrong place, the body's own cells may become damaged. Should the damage occur to DNA, the result could increase the possibility of cancer. Antioxidants decrease the damage done to cells by reducing oxidants before they can damage the cell. Antioxidants may be further classified by the products they form on oxidation (these can be antioxidants themselves, inert, or pro-oxidant), by what happens to the oxidation products (the antioxidant may be regenerated by different antioxidants or its oxidised form may be broken down by the organism, sometimes called sacrificial antioxidants) and how effective the antioxidant is against specific free radicals.