IL4 and Pruritus: Pruritus is caused by a variety of pruritus-derived cytokines, including TSLP, interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-13 (IL-13), IL-31, interleukin-33 (IL-33), etc. [140,141,142,143,144], and by the imbalance of the neuro–immune circuit between the receptors IL-4R, IL-13R, IL-31RA, OSMR, Mrgprs, and itching peptides (SP, BNP, CGRP, GRP and protease, etc.)[145,146].