The most used model of non-histaminergic itch is cowhage but this models presents several problems, such us the impossibility of standardizing the amount of the spicules inserted in the skin and the difficulty of obtaining the substance. These aspects bring us the necessity to find a new and more standardized model of non-histaminergic itch.~Papain is a cysteine protease extracted from papaya plant that is known to cause itch if applied to the skin. For these reasons the investigators would like to test a new new human itch model based on papain, and to characterize the sensory quality and temporary aspects of papain skin prick test (SPT) in comparison to the inactivated-cowhage delivery system.
In this experiment the investigators would like to test a new new human itch model based on papain, and to characterize the sensory quality and temporary aspects of papain skin prick test (SPT) in comparison to the inactivated-cowhage delivery system.