How Is Light Therapy (Phototherapy) Used To Treat Psoriasis?

Reviewed by: HU Medical Review Board | Last reviewed: June 2022. | Last updated: July 2022

Phototherapy is a type of treatment that can be used to treat people with psoriasis. It is also called light therapy. Light therapy for psoriasis is a treatment that involves exposing the skin to ultraviolet light for a specific amount of time.

What are different types of light therapy?

The main types of light therapy that are used to treat psoriasis include1:

  • UVB phototherapy
  • PUVA phototherapy
  • excimer laser therapy
  • sunlight

Some phototherapy treatments are targeted, meaning that only the skin affected by psoriasis is exposed to ultraviolet light3. Targeted phototherapy is usually used for people who have symptoms on less than 3% of the body. Whole-body phototherapy treatments expose the entire body to the ultraviolet light, and are usually used to treat patients with more severe psoriasis that affects more than 5% of the body.

Phototherapy works by affecting the skin cells in the top layer of skin, and helping to reduce psoriasis plaques to form by damaging the skin cells that cause plaques to form.

Combining phototherapy with other treatments

Phototherapy is often combined with other types of treatments for psoriasis, including certain types of systemic medicines and topical medicines3. Healthcare providers will provide specific advice about which treatments are safe to combine with phototherapy. During the phototherapy sessions, patients wear protective eyewear and shield sensitive areas of the body from exposure.

What is UVB phototherapy and how does it work to treat psoriasis?

Ultraviolet light B (UVB) is a type of light that occurs naturally in sunlight. UVB phototherapy is generally recommended for adults and children with psoriasis who have thin plaques that respond well to natural sunlight exposure1. Patients can receive UVB phototherapy in a healthcare provider’s office, or at home using a special device.

Narrow band UVB phototherapy contains a smaller range of ultraviolet light waves than broad band UVB phototherapy, which is stronger and more commonly used for more severe psoriasis. However, recent studies have suggested that narrow band UVB may have a faster effect on symptoms2.

Narrow band UVB is typically administered 3 times per week, and broadband up to 5 times per week. The length of each treatment session can depend upon the type of skin a person has3. For example, fair-skinned people need a shorter exposure time than darker-skinned people in order to avoid burning. Certain types of topical treatments can make phototherapy less effective, so let your healthcare provider know about any products you are using. Some products can also make your skin more sensitive to UVB, which can increase your risk of sunburn if they are used at the same time as UVB treatment.

Some people see benefits early on in the treatment process, while others take up to 30 treatments for peak symptom improvement. Like all types of phototherapy, UVB works best when the patient is able to stick to a consistent schedule of treatments. Some patients will stop UVB treatment when symptoms clear, while others may choose to have maintenance treatments during remission2.

Most of the side effects of UVB treatment are short-term, such as itching, burns, and blisters on the skin. Over the longer term, it can cause skin damage (similar to sun damage) and can slightly increase the risk of certain skin cancers.

What is PUVA and how does it work to treat plaque psoriasis?

Ultraviolet light A (UVA) is another type of light that occurs naturally in sunlight. PUVA is a type of treatment that combines exposure to UVA with a type of medicine that makes the skin more sensitive to light. Patients usually take psoralen in the form of a pill around two hours before the UVA treatment. Psoralen can also be administered topically in a paint or by soaking in water that contains the medicine. Some patients have side effects from oral psoralen (such as nausea), but topical psoralen is stronger and can make the skin more likely to burn1.

PUVA is usually prescribed for adults with moderate to severe psoriasis. It can help to slow down the rate at which skin cells grow and reduce symptoms. It can help lengthen the period of symptom remission for many patients2.

PUVA treatments are usually administered two or three times per week, and it can take up to 25 sessions for maximum results. Some patients benefit from combined treatment with both UVB and PUVA phototherapy.

PUVA is not used as commonly as UVB phototherapy, because it can increase the risk of developing certain types of skin cancers and cataracts, and it can cause aging of the skin when used over a longer period of time. Less serious side effects linked to PUVA treatment include itching, burns, and blisters. It is also common for white spots to develop on the affected skin once plaques have cleared3.

What is excimer laser therapy and how does it work to treat plaque psoriasis?

Another type of phototherapy treatment is delivered using an excimer laser. The excimer laser delivers a high-intensity beam of ultraviolet light. This type of phototherapy is similar to narrow-band UVB in that it specifically targets the areas of skin that are affected by psoriasis symptoms. This can help to reduce side effects because only the affected skin is exposed to the ultraviolet light1.

Excimer laser treatment is usually recommended for adults and children with mild or moderate psoriasis. It can also be effective in treating psoriasis that is difficult to reach with other types of treatment, such as symptoms on the scalp, palms, and soles of the feet. Patients generally receive treatment twice per week and generally see an effect after 4-10 treatment sessions2.

Excimer laser treatment can cause side effects including blisters, burning, and reddened skin. Because it is a relatively new type of treatment, the long-term effects of excimer laser treatment are not yet fully known (for example, the risk of skin cancer)3.

How does sunlight work to treat plaque psoriasis?

Natural sunlight contains both UVA and UVB light. Many psoriasis patients are advised to have regular, brief periods of sun exposure to help improve symptoms on affected areas. This is usually recommended for people with mild or moderate psoriasis that is not made worse by sun exposure1.

During sunlight exposure, areas of the body that are not affected by psoriasis can be protected with sunscreen or clothing. Healthcare providers will provide advice about how long to spend in the sunlight and how often, and check the patient regularly for sun damage to the skin. It can take up to a few weeks or more to see improvements from sun exposure.

Before starting treatment with sun exposure, let your healthcare provider know if you are using any topical medicines, many of which can make your skin more sensitive to light and more likely to burn. People who are being treated with other types of phototherapy may be advised to avoid sun exposure when possible2.

It is very important to protect unaffected areas from getting too much sun exposure and becoming sunburned, which can make psoriasis symptoms worse. Sunburns also increase the risk of skin cancer and can make the skin age prematurely.

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