Toxicology is the study of poisonous and harmful substances. Toxicity testing allows us to identify the toxicity of chemicals we use and gives information about the potency of their effects. As well as being true for industrial chemicals this is also true of pharmaceuticals and the natural products formed by plants, bacteria and fungi. Knowing whether a chemical can cause cancer, allergic reactions or abnormalities in unborn children is important to human health, and the process of discovering this information is known as assessment of hazard. This process is distinct from assessing risk which determines whether it is likely to actually cause harm in a given situation.