Toxicology as a scientific discipline has a very interesting and long history. The word toxicology originates from the Greek language, where “toxicon” means “arrow poison”. Most toxicologists tend to prefer to use the word “toxic” instead of “poisonous.” And, in fact, many toxicologists will tell you that there is really no such thing as a “poison” or a “poisonous” chemical”! It is the dose, frequency and timing of exposure that make a chemical ‘toxic’. Thus, typically, toxicity takes place only when a potentially toxic chemical exceeding a certain amount reaches sensitive tissues such as the reproductive organs, for example. Furthermore, toxicologists working in the related specialty of health risk assessment make the significant distinction between a chemical hazard and a chemical risk. Not all hazards pose actual risks. A chemical may be harmful or beneficial depending on the dose present, what part of the body the chemical comes in contact with, what organism is being exposed, how often and for how long, and many other considerations. Despite these seeming complexities, toxicologists approach the study of harmful properties of chemicals using relatively straightforward principles and concepts.