Phototherapy 

Patients should apply sunblock to uninvolved areas that may become exposed to UV light during the treatment session. Telling your doctor of any moisturizers and topical medications used on a regular basis might help maximize therapy, as some may affect the outcome of the treatment in a positive or negative way. For PUVA therapy, the patient takes a light-sensitizing medication (psoralen) 1–2 hours before UV treatment.

Phototherapy treatments are usually performed at a doctor's office or a psoriasis center. With the patient undressed to expose the affected areas and spare unaffected areas from the side effects of UV light, special goggles are used to prevent the risk of UV-induced cataracts. Additionally, genitalia are protected to minimize the risk of skin cancer, which is more problematic in that area. The patient stands in front of a light box lined with vertically oriented fluorescent UV lamps.

Each therapy session is supervised by a physician experienced in phototherapy treatments. The first few therapy sessions are brief in duration and are gradually increased once the patient's response to therapy is assessed. Patients with lighter skin start with shorter times of exposure compared to people with darker skin.