Phototherapy is when your dermatologist (skin doctor) uses ultraviolet (UV) light to treat your psoriasis. It works because UV light reduces the inflammation of your skin helping to clear, but not cure, your psoriasis.
A course of phototherapy can vary in duration, depending on what type you receive. Some types last around 8–10 weeks while others need up to 16 weeks. You will need to go into the Phototherapy Unit in hospital two or three times a week to receive it.
You will be treated with either UVA or UVB light. UVA reaches deeper layers of skin and so is used for more severe psoriasis, but is more likely to have side effects. With UVA (also called PUVA) treatment you will need to take a tablet or take a bath with a sensitiser called psoralen.
You may not be able to have phototherapy if you can’t attend the sessions, if you are taking medicine that suppresses your immune system, or makes your skin more sensitive to sunlight, or if you are pregnant (only UVA).
The side effects are generally short-lived such as sunburn, dry, itchy skin, rash, and blisters where your psoriasis appears. Psoralen may also make you feel sick, and in some cases, your psoriasis might get worse before it gets better. There are also some longer term side effects that your doctor will discuss with you.