An elevated IL-31 mRNA in the skin and increased serum levels of IL-31 are found in subjects with allergic contact dermatitis, atopic dermatitis, prurigo nodularis, chronic spontaneous urticaria, mastocytosis and primary cutaneous lymphoma and in some of these conditions IL-31 levels correlate with disease activity, as a diagnostic marker of severity in allergic diseases [32]. The gene discussed is IL31; the disease is prurigo nodularis.