Light therapy, or phototherapy, can improve the symptoms of psoriasis in many people. It 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.

However, it may not be suitable for everyone. One possible drawback is that long-term exposure to light therapy can increase the 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 a qualified health professional shining ultraviolet (UV) light on the skin.

It can help manage psoriasis by:

  • slowing the overgrowth of skin cells, which reduces psoriasis plaque formation
  • suppressing the immune system
  • reducing inflammation
  • allowing the skin to heal
  • decreasing or eliminating itching

In some cases, it may remove plaques entirely.

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

Depending on which areas psoriasis affects, a person can have phototherapy on one area, such as the hands or scalp, or across the whole body.

On the day of the appointment, the American Academy of Dermatology (AAD) urges anyone having UVB treatment to avoid applying salicylic acid, as it may reduce the effectiveness of the treatment.

Before treatment, a healthcare professional will protect sensitive skin areas, such as the eyes and genitals. They may ask you to bring a factor 50+ sunscreen to apply before treatment.

The health professional will then either ask the person to stand in a lightbox or apply the light directly to the skin.

If a person is having UVA light exposure, they will have treatment with psoralen before starting. This may be in a bath soak, as a cream, or as tablets taken beforehand. This treatment — psoralen plus UVA — is called PUVA phototherapy.

Doctors often recommend three sessions per week of phototherapy over 4–12 weeks, but a person may have up to 5 treatments per week.

As the sessions progress, the length of exposure time will increase. Between sessions, the skin will have time to heal.

Research suggests light therapy may help manage:

  • small areas of stubborn, thick plaque psoriasis
  • long-term palmoplantar psoriasis
  • plaque psoriasis over a wide area of the body
  • nail psoriasis
  • scalp psoriasis

One study has also concluded that narrow-band UVB exposure is effective against a rare type of psoriasis called acute guttate psoriasis.

Research suggests that 50–90% of people see either a noticeable improvement or complete remission with light therapy, although symptoms will likely reappear at some time.

However, people’s skins react differently, which can affect how much improvement they see and how long the benefits last.

Light therapy may not be effective if a person misses appointments. The AAD suggests that attending 3–5 sessions per week produces the best results.

Which type is best? PUVA, narrow-band or broad-band UVB?

Types of phototherapy may vary in effectiveness.

PUVA currently appears to be more effective than UVB therapy, although it entails a higher risk of adverse effects and skin cancer.

UVB treatment can be broad-band or narrow-band, depending on the range of UV light the bulb produces. Narrow-band is more commonly used than broad-band.

With narrow-band UVB, the symptoms may clear more rapidly and stay away for longer. The person may also need fewer weekly treatments than with broad-band UVB, according to the National Psoriasis Foundation.

UVA with psoralen, or PUVA, can penetrate to deeper levels of the skin.

UVB has a shorter wavelength and only reaches the upper levels of the skin. It does not need psoralen. Currently, UVB treatment appears to entail a lower risk of skin aging and skin cancer compared with PUVA.

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

Factors to consider

A healthcare professional will discuss the options with the individual based on the following factors:

  • how much of the body the psoriasis affects
  • where symptoms occur on the body
  • how much psoriasis affects an individual’s quality of life
  • a person’s overall health
  • a person’s skin type

What are the types?

The different types of light therapy for psoriasis include:

  • Narrow-band UVB is the most common type and less likely to produce adverse effects.
  • Broad-band UVB is an older form of light therapy.
  • Laser UVB uses a smaller beam of UVB that can target smaller areas, such as the scalp.
  • Topical PUVA involves either soaking in a bath or applying a lotion containing psoralen followed by UVA treatment.
  • Oral PUVA involves taking psoralen pills 40–60 minutes before phototherapy.
  • UVB phototherapy at home is when physicians prescribe follow-up treatment with hand-held or smaller-scale lightboxes for ongoing management of symptoms at home.
  • Balneophototherapy involves undergoing UV light treatment either during or immediately after bathing in a salt-based solution.
  • Pulsed dye laser (PDL) may be useful for small lesions on the surface of the skin or nail psoriasis.
  • A blue light device is a wearable device for home use. It does not use UV light but may help manage mild psoriasis on the arm or leg, wherever a person wears it.

A dermatologist may recommend light therapy for people with moderate to severe psoriasis whose symptoms are not responding to creams and lotions.

Light therapy may not be suitable for people who:

  • are using medications that increase photosensitivity, such as antihistamines or antifungals
  • have a history or high risk of skin cancer
  • have lupus or porphyria, which increase a person’s sensitivity to light
  • have other photosensitivity issues

Talk to a healthcare professional about any current supplements or medications before having phototherapy. During pregnancy and breastfeeding, only UVB may be suitable.

Depending on a person’s known sensitivity to UV light, a doctor may not recommend light therapy.

However, even people with no known sensitivity may experience:

  • mild sunburn
  • a stinging or itching sensation
  • skin changes such as dark spots or wrinkling
  • blisters
  • an increased risk of skin cancer

For people receiving PUVA, experts recommend limiting the lifetime usage to 150 sessions to lower the risk of skin cancer. This may also be true for UVB therapy, but researchers are still looking into it.

People receiving UVB treatment should undergo a review after 500 sessions.

Blue-light treatment is a milder option but is unlikely to cause skin cancer or early skin aging as it does not produce UV rays.

Here are some questions people often ask about light therapy for psoriasis.

Is light therapy good for psoriasis?

Light therapy may help manage severe plaques and widespread plaque psoriasis as well as nail, scalp, and palmoplantar psoriasis. However, the effectiveness may depend on the extent and type of treatment.

Which type of light therapy is best for psoriasis?

A dermatologist can help an individual decide on the best option, depending on their symptoms, any history of skin cancer, medication use, and other factors. Psoralen with UVA (PUVA) appears to be effective in many cases, but there may be a higher risk of adverse effects than with other types.

Is blue or red light good for psoriasis?

Blue and red light do not include UV rays, which makes them a milder option. One older study concluded that blue light was likely more effective than red light. Wearable blue light devices now have approval for treating mild psoriasis at home.

Phototherapy can help manage the symptoms of psoriasis. However, the options and effectiveness will depend on factors such as the type and extent of psoriasis, any history of skin cancer, other health conditions, and medication use.

Anyone undergoing extensive phototherapy treatment would benefit from a regular skin check to ensure there are no unwanted changes that could indicate skin cancer.