Light therapy for psoriasis: Types, effectiveness, and side effects

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.

What is light therapy for psoriasis?

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.

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.

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.

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