Psoriasis phototherapy usually refers to narrow-spectrum medium-wave ultraviolet therapy, abbreviated as NB-UVB. the initial dose of UVB is usually 75%-100% of the suberythematous amount, usually 2-4 times per week, and significant results can be seen in about 4-8 weeks. It is also effective for plaque psoriasis, but its effect and remission period are not as good as PUVA. psoriasis phototherapy can cause side effects such as erythema and hyperpigmentation, but it can avoid adverse reactions such as nausea, headache and dizziness produced by photosensitizers, and its carcinogenicity is also lower than PUVA. psoriasis phototherapy can also be combined with other drugs to treat moderate and severe psoriasis .