Generally, a person undergoing phototherapy will expose their skin to UVB on a regular schedule — typically starting with a so-called “initial clearance series” of two to three times a week for three to four months, for a total of about 24 to 30 sessions, says Sobel. 

Your dermatologist will determine the initial UVB dose by assessing your skin type, then gradually increase the amount. This treatment is performed on-site in a medical setting like a clinic or hospital.

While the exposure to UV light usually doesn’t take long (several seconds to a few minutes), appointments generally last about 15 minutes or more, with precautions taken before and after exposure. 

You’ll wear protective glasses during the treatment as well as protective coverings for sensitive parts of the body such as your face and genitals.

After treatment, a nurse will give you moisturizer to apply to your skin (and can help you apply it in hard-to-reach areas).Treating psoriasis with at-home light therapy can be a convenient and affordable option for some people, says Richard. “I recommend getting the equipment from a reputable vendor; there are several manufacturers that provide home phototherapy and require a medical prescription from a provider,” she says. Richard doesn’t recommend picking equipment from an online vendor that doesn’t require a doctor’s prescription.

At-home light therapy should be performed under the supervision of a doctor, and as with in-office phototherapy, you should have a skin cancer screening each year, Richard says.

Preparing for UVB Phototherapy

To determine if UVB phototherapy is a good option for you, you’ll have an initial consultation with a dermatologist. Your doctor will determine the wavelength and dose of the light, as well as how long your treatment will last.

You’ll want to bring a list of all current medications, including any supplements, you’re taking, as this can affect how sensitive your skin is to UV light.

Don’t wear any lotions or fragrance to your treatment sessions, as these can make your skin more sensitive.

The AAD cautions against applying salicylic acid, an exfoliator, beforehand. It can make UVB phototherapy less effective.

After each treatment, your skin should be a little red or pink, notes the AAD. And following your phototherapy session, you’ll want to minimize irritating your skin. Use a mild soap or cleanser when showering. Keep showers short and limit them to once a day. Water can be warm but not hot.

Thoroughly moisturize your skin at least twice a day, ideally right after showering.

Potential Side Effects and Risks

There are risks and side effects associated with light therapy, says Richard. “The main short effect of phototherapy is that if the dose is increased too rapidly, you can get a sunburn-like reaction. There are protocols in place to increase the dosing in a stepwise fashion to minimize that risk,” she says.

Other possible immediate side effects include:

Mild stinging or burning Dark spots on the skin (more likely in people with medium to dark complexions) Itching Blistering is a rare but possible side effect, too.

As far as long-term side effects, light therapy can accelerate photoaging, which is premature aging of the skin, says Sobel. Photoaging causes things like an increase in freckling or dryness of the skin, he adds.

Skin cancer is another concern with phototherapy. “While studies haven’t shown an increased risk of skin cancer, as with any UV exposure we do recommend that skin cancer screening be performed annually for patients who are on phototherapy,” says Richard.

Your dermatologist can manage long-term side effects with you. Your doctor will also monitor your progress and you’ll have a checkup after a certain number of treatments — typically after four to six, notes the AAD. Be sure to tell your doctor about any side effects you may be experiencing.

The Take away Phototherapy can be a safe and effective treatment for psoriasis, helping ease symptoms by using controlled ultraviolet light to calm the overactive immune response in the skin.

Talk with your healthcare provider to see if phototherapy might suit your needs, particularly if you're looking for a noninvasive psoriasis treatment option.