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What is Psoriasis Light Therapy?

By K. Willis
Updated: Mar 03, 2024

Psoriasis light therapy involves using two strains of ultraviolet light, UVA and UVB, to reduce psoriasis, a condition in which the production of skin cells is accelerated. Sunlight has been used to treat psoriasis for more than a century. The only types of ultraviolet light that have proved beneficial in the treatment of psoriasis are UVA and UVB.

Skin cells usually take between 21 and 28 days to replace themselves, but this process speeds up to two to six days in psoriasis sufferers. Psoriasis presents as psoriatic plaque, which is raised, red areas of skin caused by the increased number of blood vessels required to accommodate the increase in cell production. These red areas are covered with silvery-white "scales," an accumulation of skin cells waiting to be shed.

Psoriasis plaque most commonly occur on elbows, knees, the lower back and scalp, but it can occur anywhere on the body. Psoriasis also can occur in more sensitive areas such as the groin, genitals and underarms; these areas usually don't have scales but are raised and red. Psoriasis can be painful, itchy and sore and, in severe cases, can crack and bleed.

Phototherapy is the term given to psoriasis treatment using ultraviolet light. For UVA to be beneficial in the treatment of psoriasis, it must be combined with psolaren, a chemical agent that makes skin more sensitive to UVA. This combined treatment, called PUVA, was introduced in the 1970s. Psolaren can be taken in tablet form or as a bath oil, ointment or lotion. After a set time determined by a health professional, the skin is then exposed to UVA radiation in a radiation cabinet, which is similar in appearance to a shower cubicle, or with the use of a small, portable unit depending on the size of the area requiring treatment.

Protective eye glasses must be worn when psolaren treatment begins to prevent damage to the eyes, which also become more sensitive to UVA with the use of psolaren. The glasses must be worn even indoors, because UVA is able to penetrate glass. It can take up to three months of treatment before improvement in the appearance of the psoriasis can be seen. Once treatment is complete, the skin can remain clear of psoriasis for up to six months.

Psoriasis light therapy using UVB has been in use since the 1920s. UVB is recommended for psoriasis that has not responded to other treatments. It is the wavelength of sunlight responsible for causing the most sunburn. The wavelength of UVB that is beneficial in psoriasis light therapy is a very narrow band between 300 and 313 nanometers. UVB therapy is administered inside a radiation cabinet via ultraviolet light tubes. Sunglasses must be worn inside the cabinet to prevent eye damage.

Because extended exposure to ultraviolet light can have potentially serious side effects, the amount of ultraviolet light must be carefully and precisely calculated by a health professional. Psoriasis light therapy usually lasts for periods between six and 12 weeks, depending on the type of light therapy, with treatments up to three times each week and at least 48 hours between treatments to allow the skin time to recover. Potential side effects from the use of psoriasis light therapy include sunburn, itching, dry skin, freckles, premature skin aging and skin cancer. Moisturizer should be applied liberally after each treatment to minimize dryness and itching. Persistent itching or burning sensations should be brought to the attention of a health professional as soon as possible.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
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