Thus, while acute high dose UVB increased IL-31 and pruritus, repeated lower doses of UVA-1 and NB-UVB appear to reduce IL-31 and pruritus, and it may be speculated that IL-31 reduction in the skin may contribute to the antipruritic effect of phototherapy in AD, in psoriasis, and maybe other pruritic conditions, e.g., chronic prurigo and CTCL, in which increased IL-31 or its receptor appear to play a role in chronic pruritus. The gene discussed is IL31; the disease is Alzheimer disease.