ABSTRACT
The classification of chemical agents is a daunting task considering the vast number and complexity of chemical compounds in the public domain. With the variety of chemicals and drugs available, and their varied pharmacological and toxicological effects, an agent may find itself listed in several different categories. The European Union established regulations addressing the assessment of all relevant industrial chemicals concerning the registration, evaluation, authorization, and restriction of chemicals. The immune system, and the mechanisms by which the body maintains homeostasis and protection against microorganisms, is often the target of chemical agents and therapeutic drugs. The liver is a target organ for many chemicals and therapeutic drugs, predominantly as a result of its high metabolic capacity, extensive circulation, and sizeable surface area. The skin boasts the largest surface area of any organ and has traditionally been understood as the first line of defense against microbial and xenobiotic insult.
