The Many Challenges of Human Experimental Itch Research

Itch has long been a neglected sense within somatosensory research, and with good reason: acute itch, although relatively easy to trigger, is notoriously difficult to control experimentally. Its time course and behavior cannot easily be predicted and participants find it difficult to quantify (and indeed qualify) the sensation. Even scratch behavior in response to itch is weakly correlated to the amount of itch someone is experiencing. This chapter will focus on the three main methods of acute, experimental itch induction: chemically evoked itch (through histamine and cowhage), mechanically or electrically evoked itch, and psychologically evoked itch (through visual and auditory means). The basic materials and experimental designs will be described along with our personal experiences of trying to study itch using these methods. Itch research is not for the faint-hearted; there are more failures along the road than successes. We do it because itch remains one of the most elusive and fascinating areas of somatosensory research. It can give excruciating pain or intense pleasure with just a single scratch and unlocking its mysteries will help the countless thousands who experience debilitating pruritic skin conditions such as eczema, atopic dermatitis, and psoriasis