Cowhage-evoked itch is mediated by a novel cysteine protease: a ligand of protease-activated receptors.

Cowhage spicules provide an important model for histamine-independent itch. We determined that the active component of cowhage, termed mucunain, is a novel cysteine protease. We isolated mucunain and demonstrate that both native and recombinant mucunain evoke the same quality of itch in humans.