Does light therapy (phototherapy) help reduce psoriasis symptoms?

The type of light therapy that is generally used to treat psoriasis is known as narrow band UVB phototherapy. Here the skin is only exposed to UVB light wavelengths between 311 and 313 nanometers. The idea is that limiting the light spectrum in this way reduces the risk of side effects.

Another kind of light therapy is known as balneophototherapy. Here people bathe in warm water containing specific substances for about 20 minutes. Their skin is exposed to artificial UV light while bathing, or immediately afterwards. The bath often contains a solution made out of common salt or Dead Sea salt.

There is also another option called “psoralen plus ultraviolet A” (PUVA) therapy. It involves exposing the skin to UVA light and using a medication known as "psoralen" too. The medication makes the skin more responsive to UVA light, increasing its effect. Psoralen can be taken as a tablet, applied to the skin in the form of a gel or cream, or added to a bath.

Before the treatment starts, the wavelength and dose of the light used have to be determined, as well as the duration of treatment. Many different factors play a role here, including what kind of skin you have, whether you have had other medical conditions such as skin cancer, and whether you are taking medication that makes your skin more sensitive to light. It is important to be treated by a skin specialist (dermatologist) who knows how to carry out light therapy.

The treatment can last between four weeks and three months. In order to allow the skin to get used to the radiation, the initial dose is determined based on the patient's skin type and then gradually increased.

During the treatment the patient's eyes are protected with special sunglasses. Sensitive parts of the body that aren't affected by psoriasis, such as the face or genitals, are covered up to protect them. Alternatively, the healthy skin can be protected by applying SPF 50+ sunscreen.

UV light therapy can have various side effects. For instance, the radiation can dry out your skin and cause itching. So people are advised to thoroughly moisturize their skin with a lipid-replenishing skin care product immediately after the treatment. Light therapy also often causes sunburn-like skin reactions. In rare cases, blistering burns may occur.

In people who tend to get cold sores on their lips, light therapy might make cold sores more likely. Applying sunscreen to your lips before the treatment can help prevent cold sores. Taking psoralen for PUVA therapy can cause nausea and vomiting. These side effects don't occur when psoralen is used as a bath solution.

Other, less common, side effects include raised red patches that go away again after a few days and hair follicle infections.

In order to limit side effects as much as possible, it's important to avoid natural sunlight on the day of treatment, or protect yourself when outdoors by wearing appropriate clothing, sunglasses and sunscreen. It is particularly important to avoid further exposure to sunlight after PUVA therapy.

Another disadvantage of UV light therapy is that it involves a lot of doctors' appointments and takes up a lot of time overall. So people who are busy, for instance with their work and family, might find it hard to stick to this treatment in everyday life.

Regular exposure to UV light increases the risk of skin cancer. There is some evidence that PUVA therapy with psoralen tablets in particular increases the risk of non-melanoma skin cancer. The higher the dose of radiation used and the more light therapy sessions you have, the greater the risk. The risk is also higher in people who have a fair complexion, people who have had skin cancer in the past, and people who are taking medication to suppress their immune system (immunosuppressants) such as azathioprine, ciclosporin or methotrexate.

Narrow band UVB phototherapy is probably associated with a lower risk of skin cancer than PUVA therapy using psoralen tablets. But this isn't yet known for sure because there are hardly any studies on the risk of skin cancer caused by UVB radiation. There is also a lack of good research on the risk of skin cancer associated with PUVA therapy using psoralen that is added to a bath or applied directly to the skin.

To limit the risk of skin cancer, people are advised not to have more than 150 sessions of PUVA therapy using psoralen tablets in their lifetime. A "UV diary" can help you keep track of the number of sessions and type of light therapy you have had, as well as the radiation dose used.

Light therapy is often an effective treatment for psoriasis: It is estimated that the symptoms improve noticeably or go away completely for a while in 50 to 90 out of 100 people.

It is currently thought that PUVA using psoralen tablets is more effective than narrow band UVB phototherapy. But side effects are also more common and the associated risk of skin cancer may be greater. So it is a good idea to talk to your doctor and carefully weigh the pros and cons of PUVA therapy using psoralen tablets.

PUVA therapy using psoralen added to a bath has also been shown to relieve psoriasis symptoms more effectively than UVB phototherapy alone. And light therapy combined with bathing in a solution of common salt or Dead Sea salt appears to be more effective than UV light therapy without bathing, but it is less effective than PUVA therapy using psoralen added to a bath. PUVA therapy using psoralen tablets, PUVA therapy using a psoralen bath solution, and light therapy combined with bathing in a salt solution all share one common disadvantage: the effort involved.