phototherapy machine at dermatologist's office

What You Need to Know About Phototherapy for Psoriasis

By Leah Campbell
September 09, 2021

As you review your treatment options for psoriasis, your doctor may suggest you consider phototherapy. This is a prescription treatment that involves medically supervised exposure to ultraviolet light. But how exactly does phototherapy work to help psoriasis? What are the appointments like? And what are the pros and cons to consider? We’ve got all that info and more to help you make the right decision.

Phototherapy: A Natural Option

“There is nothing more natural than light therapy,” says Susan Bard, M.D., a board-certified dermatologist at Vive Dermatology in Brooklyn, New York.

According to Bard, phototherapy was developed because “people literally noticed their psoriasis was better in the summer when exposed to sun.”

She joked that while she’d love to say it came about because dermatologists are that brilliant, it was just a matter of cause and effect. “I think it’s been long-standing knowledge that sun is good for psoriasis.”

How Does Phototherapy Work?

“Sunlight generally has a small immunosuppressant effect on the skin,” explains board-certified dermatologist Dina Began, M.D., of The Dermatology Specialists in New York City. “Phototherapy allows us to leverage that benefit in a more localized and dose-specific way.”

The advantage of phototherapy is that it’s more controlled than just going out into the sun. For it, consistent treatments are administered in a clinical setting, with very specific wavelengths of UVB light and for a set period of time.

Wondering why UVB? Well, while the sun emits both ultraviolet A (UVA) and ultraviolet B (UVB) rays, UVA accounts for most of what we are exposed to outdoors. But UVB phototherapy harnesses UVB rays to help slow the growth of psoriasis cells. There are also PUVA (psoralen and UVA) treatments available, which combine UVA phototherapy sessions with a medication that helps increase light sensitivity in order to improve the overall results.

One of the benefits to phototherapy over direct sun exposure is the ability to target treatment areas. “We’re able to specifically treat the areas where inflammatory mediators are revved up in the epidermis and dermal layer over the skin, and the light helps bring the inflammation down to a more normal baseline level,” Began explains.

The treatment itself is medication-free and can be done quickly, requiring just a few minutes two to three times a week, according to Bard.

What Can I Expect with Treatment?

Phototherapy sessions typically occur two to three times a week for at least two to four months. The type of therapy prescribed (UVB or PUVA), the duration of treatment, and the level of UV light used will all depend on several factors, including your skin type and the severity of your psoriasis.

You’ll be asked to avoid using skin moisturizers for 24 hours before your treatment, and will be provided with protective goggles to keep your eyes safe during treatment. You’ll be advised to cover any areas that do not need treatment and you may want to consider using sunscreen on unaffected skin that will be exposed.

Depending on the equipment available and the area of skin that needs to be treated, you may be asked to step into a large, full-body unit. Or you could be treated with a smaller, handheld unit that’s able to target a specific area of the body.

While receiving your treatment, you may experience a warming of the skin, similar to being outside on a hot, sunny day.

In some cases, patients can obtain home phototherapy systems. But even then, the specifications for how this treatment should be administered are precise.

What Are the Risks?

“I warn everyone that even though we use a very specific wavelength for a very limited timeframe, this is still radiation,” Bard says, of phototherapy.

Began agrees. “The downside of phototherapy, and sunlight in general, is that it can cause photo damage, photoaging, and an increased risk of skin cancers.”

She says that the precise delivery system phototherapy units provide help to minimize those risks and maximize the benefits. Still, “if patients have a family history of melanoma, dysplastic nevi [large, irregular moles], pre-existing photo damage or photoaging, or other nonmelanoma cancers, it’s advisable to avoid phototherapy altogether or to use it with caution.”

Bard says the other potential downside of phototherapy is financial. “It can be costly if you have a high co-pay,” she says. “And a home unit may not be covered by insurance.”

Don’t DIY

Given the high cost and time commitment of seeing the doctor, it might be tempting to take matters into your own hands with outdoor sun exposure or tanning beds. But both Bard and Began strongly advise against this. When doing phototherapy, it’s important to follow a doctor’s orders.

“Tanning beds don’t have the same level of protection and specificity,” Bard says. “If you’re not being carefully monitored, you’re more likely to burn. And anytime you traumatize your skin, you have now created a new area where psoriasis could occur.”