Several neuropeptides, including substance P (SP), nerve growth factor, calcitonin gene-related peptide, and vasoactive intestinal peptide have been hypothesized to play a part in the development of psoriasis and its symptoms.
Overexpression of several genes, such as phospholipase A2 IVD, substance P, voltage-gated sodium channel 1.7, and transient receptor potential (TRP) vanilloid 1, in itchy skin was positively correlated with itch intensity ratings in both atopic dermatitis and psoriasis.
A hypothesis for the role of substance P that would account for the temporal onset with stress, the clinical symmetry of lesions, and the histopathologic features of psoriasis is presented.