What is the best treatment for severe psoriasis? Photochemistry can help.

The risks of long-term UVB use are the same as exposure to the sun: skin cancer and skin aging. But long-term studies have shown that skin cancer rates are not increased in a large number of patients treated with UVB, meaning that UVB therapy is safer than sunlight. For this reason, UVB therapy is considered one of the least risky and most effective treatments for moderate to severe psoriasis. Your doctor will need to make regular checks on your skin.　　Home light therapy (UVB) Some patients should get a prescription from their doctor before getting UVB equipment, and the treatment process must also be fully supervised by a doctor.　　Photochemotherapy (PUVA) PUVA (short for PsoralenwithUltraVioletALight) is used to treat moderate to severe psoriasis, as well as disabling psoriasis that cannot be controlled by other methods. Psoralen is a medication that is activated in the skin by ultraviolet light (UVA).PUVA can be used all over the body or on specific areas of the skin, such as the hands and feet. It can also be used in combination with other treatments.　　PUVA needs to be administered under medical supervision and there are also several ways to administer it. The most common method involves the patient taking oral medication and then irradiating the affected area with UVA.The key to success with PUVA is time control.　　Other methods of PUVA are the topical application of medication: the application of Retropiprazole directly on the affected area, especially on the palms of the hands and soles of the feet; the immersion method in which the affected area, such as the hands or feet, is immersed in a tub containing psoralen; and the bathing method, in which the whole body is immersed in the psoralen in the bathtub.　　PUVA is recommended for patients with moderate to severe psoriasis, or for those who have used other methods without success. Patients who are psychologically or mentally disabled by the disease and elderly patients also use PUVA as a primary treatment.　　Common side effects of short-term use of PUVA include stomach upset and red, itchy skin. Long-term use increases the chances of developing skin discoloration, premature skin aging, and cataracts. No cataracts have been reported to date with the use of appropriate eye protection.