Light therapy, or phototherapy, can improve the symptoms of psoriasis in many people. Light therapy works by reducing skin inflammation and slowing down the production of skin cells.

Doctors may recommend light therapy when a person has moderate to severe psoriasis, or psoriasis that has not responded to other treatments.

Along with its benefits, however, light therapy has side effects. Repeated and long-term exposure to light therapy can increase a person’s risk of skin cancer.

In this article, we take a close look at light therapy for psoriasis, including its types, effectiveness, and possible side effects.

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Light therapy involves shining ultraviolet (UV) light on the skin, which can reduce the size, itchiness, and appearance of plaques. It may even clear them up entirely.

Light therapy does not cure psoriasis, but it can help people manage their condition and improve their quality of life.

Light therapy for psoriasis works by slowing down the excess growth of skin cells, which reduces plaque formation. It also limits the growth of skin cells by affecting the functioning of the DNA.

Light therapy procedure

Depending on which areas the psoriasis affects, a person can get phototherapy on one area, such as the hands or scalp, or across their whole body. A healthcare professional will protect sensitive skin areas, such as the eyes and genitals, before treatment.

Light therapy requires multiple sessions to gradually increase the amount of time the skin is exposed to UV light, and to give it time to heal.

People usually undergo three to five light therapy sessions per week over the course of 2–3 months. People usually see an improvement in 2–4 weeks, depending on the type of light therapy.

Each person’s skin reacts to phototherapy differently, both in how much improvement they see in their psoriasis symptoms and in how long those benefits last. The average remission time is 3–12 months.

Because of the increased risk of skin cancer, doctors advise people to limit their lifetime usage of psoralen and ultraviolet A (PUVA) phototherapy to 150 sessions.

Light therapy is effective for reducing or clearing up the symptoms of psoriasis.

An estimated 75 percent of people using narrow-band ultraviolet B (UVB) therapy, which is the most common type, will develop clear skin. This will last for at least 6 months.

Research has found that narrow-band UVB treatments are effective against a rarer form of psoriasis called acute guttate psoriasis, and that people were satisfied with this treatment.

According to the Institute for Quality and Efficiency in Health Care, using light therapy to treat psoriasis results in noticeable improvement or a complete reduction of symptoms in 50–90 percent of people.

There are many different ways to deliver light therapy for psoriasis, including different types of light and equipment.

A healthcare professional will choose which phototherapy method to use based on the following factors:

  • how much of the body the psoriasis affects
  • which body parts psoriasis affects
  • how much psoriasis affects an individual’s quality of life
  • a person’s overall health
  • a person’s skin type

One key difference between the various forms of phototherapy is the type of UV light used in treatment:

  • UVA has a long wavelength. It can go through glass windows and penetrate to deeper levels of the skin. People must use UVA treatments in combination with psoralen, which makes the skin more receptive to the UVA rays.
  • UVB has a shorter wavelength. It only reaches the upper levels of the skin and does not require psoralen.

The different types of light therapy for psoriasis include:

  • Narrow-band UVB. Narrow-band phototherapy, the most common light therapy, limits the light wavelengths used in treatment to 311–313 nanometers, to keep possible side effects in check.
  • Broad-band UVB. Broad-band phototherapy is the oldest form of light therapy for psoriasis. It uses a wider wavelength than narrow-band therapy.
  • Laser UVB. Laser techniques use a smaller, more targeted beam of UVB. Healthcare professionals prefer this technique when psoriasis affects less than 5 percent of the body.
  • Topical PUVA. With PUVA, a person either soaks in a bath or applies a lotion containing psoralen, which makes the skin more receptive to the UV light treatment that follows.
  • Oral PUVA. With oral PUVA, a person takes pills containing psoralen before phototherapy. This form of treatment may be especially helpful for very thick plaques.
  • Pulsed dye laser (PDL). Healthcare professionals most often use PDL for small lesions on the surface of the skin or nail psoriasis.
  • Balneophototherapy. Here, a person will undergo UV light treatments either while bathing in a salt-based solution or immediately afterward.
  • Low-level light or laser therapy. Sometimes called “cold laser” treatment, doctors also recommend this treatment for other forms of inflammation and chronic pain.
  • UVB phototherapy at home. Physicians may prescribe at-home follow-up treatment, with individuals using hand-held or smaller-scale light boxes to stay on top of their psoriasis and manage any increases in itchiness and plaques, or “flares.”

A doctor or skin specialist, called a dermatologist, may recommend light therapy if creams and lotions are not enough to control psoriasis symptoms.

People with moderate to severe psoriasis may benefit from light therapy. In moderate psoriasis, the condition affects 3–10 percent of the body, while severe psoriasis affects more than 10 percent of the body.

People who take medications and over-the-counter supplements that make their skin more sensitive to UV radiation should not undergo phototherapy.

These photosensitizing medications include:

  • antihistamines
  • contraceptives
  • diuretics
  • sulfa drugs

Talk to a healthcare professional about any current supplements or medications before agreeing on phototherapy.

Pregnant women should avoid light therapy for psoriasis, as should people with:

  • a history of skin cancers, both melanoma and non-melanoma
  • a depressed immune system
  • lupus
  • known photosensitivity issues

A healthcare professional will consider a person’s sensitivity to UV light when planning a course of phototherapy. Despite this precaution, people can still experience side effects.

Possible side effects of light therapy include:

  • mild sunburn, which typically is not serious and is possible to resolve by changing the UV dosage
  • a stinging or itching sensation
  • an increased likelihood of cold sores in people prone to them
  • signs of premature aging of the skin, such as dark spots and loose or leathery skin
  • blisters
  • an increased risk of skin cancer

There is no cure for psoriasis, but with treatment, people are able to control their symptoms and improve their quality of life.

Phototherapy can be extremely helpful for people who have moderate to severe psoriasis.

Due to the potential for a greater risk of skin cancer, people undergoing extensive phototherapy treatment should have their skin examined regularly by a physician.