ABSTRACT
The specificity of the sensation of itch has been debated continuously since Johannes Muller formulated his theory of specific nerve energies in the 19th century. Initial investigations ignored itch, but von Frey (I) identified "itch spots" in the skin using punctate mechanical stimuli. As these itch spots seemed to coincide with pain spots, some considered that itch was a subliminal version of pain. The question of whether itch is a specific sensation or whether it arises from weak activation of pain pathways might seem trivial to those whose experience of itch is confined to the minor annoyance of a mosquito bite, but severe, intractable itching that is resistant to conventional drugs is a symptom of several systemic diseases induding biliary cholestasis, renal failure, HIV infection, and immune disorders.
