Our body defends itself from toxicity by detoxifying potentially harmful substances that are made in the body, that invade our environment, or that are found in our diet. Toxic metabolites and foreign chemicals can be produced endogenously as byproducts of normal metabolism (e.g. hormones), or can be ingested in pharmaceutical, industrial, and environmental chemicals, food additives, or cooking byproducts (i.e. nitrates, polycyclic aromatic hydrocarbons). Many of these substances must be detoxified by the liver in order to become inactive and excreted from the body.