In the present study, we measured plasma levels of dynorphin A and β-endorphin as well as serum levels of LCN-2, MMP-9, and the MMP-9/LCN-2 complex and investigated their relationships with itch severity in pruritic skin diseases, such as AD, PSO, prurigo nodularis (PN), urticaria, palmoplantar pustulosis (PPP), and asteatotic dermatitis (AsD). This evidence concerns the gene MMP9 and prurigo nodularis.