Phototherapy, or light therapy, involves exposing the skin to ultraviolet light on a regular basis. Treatments can be done at a doctor’s office or at home with a special light unit. Present in natural sunlight, ultraviolet B (UVB) is an effective treatment for psoriasis according to the National Psoriasis Foundation. During UVB treatment, your psoriasis may worsen temporarily before improving. It can take several weeks to see overall improvement.