Abstract
Itch is a common sensation and a component of numerous disease states. Itch can be classified according to its origin and may be modulated by both endogenous and exogenous factors. The purpose of this chapter is to classify the common causes of exogenous itch in humans. These factors were classified into mechanical, chemical, and environmental components. A better understanding of the various mechanisms of pruritus is critical to effective research into the treatment of itch.