Beneath the Surface

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What is phototherapy, and how does it work?

By Charlene V. Kakimoto, MD
Chief Medical Officer, Clarify Medical

Light therapy, also known as phototherapy, is the use of ultraviolet (UV) light for its healing effects. Phototherapy has been used worldwide for nearly a century to treat chronic skin conditions such as psoriasis, vitiligo and severe eczema.

While many treatments decrease the overall immune system, UV light can be used to decrease the local immune system in the skin. In conditions such as psoriasis, light therapy can also slow down the development of thick, scaly skin. UV light therapy is used in vitiligo for its additional ability to stimulate melanocytes, the skin’s pigment-producing cells. This makes phototherapy a nice treatment option for just about anyone—especially those who don’t like creams, those wanting a natural treatment, a steroid-free treatment, and those wanting additional control using a combination of therapies. Phototherapy is also a good option to consider for children and women during pregnancy.

Is phototherapy safe?

Dermatologists consider NB-UVB light therapy to be safe when it’s used responsibly.

In the few human studies evaluating this concern, an increased incidence of skin cancer has not been established. In the largest study to date in which 3867 psoriasis patients were treated with NB-UVB, with the median number of treatments being 29 and with 352 patients receiving more than 100 treatments, there was no significant association found with basal cell carcinoma, squamous cell carcinoma or melanoma. The median follow-up period was 5.5 years.

However, we need additional studies looking at what happens beyond that timeframe. And we need to take into consideration that newer, targeted forms of phototherapy like the Clarify System, have recently been developed. Targeted therapy is designed to focus healing light to the affected skin, sparing unnecessary light going onto surrounding skin. With recent advances in photomedicine and when used in combination with other therapies, healing can occur sooner and thus reduce overall UV exposure. Sunlight and tanning beds contain UVA which can damage the deeper layers of your skin. The Clarify Handheld light technology filters out UVA and only emits NB-UVB, which helps to reduce the potential for long-term side effects like skin cancer to develop over time.

Experts do agree there is likely an association with NB-UVB and the development of nonmelanoma skin cancer. Thus, a prescription for these treatments is required by law in the United States and many other places. So before you use a phototherapy treatment, it is recommended that you discuss all of the benefits and potential side effects. Together you and your physician can make an informed decision.

How often is phototherapy needed?

Phototherapy treatments are typically administered three times a week. In psoriasis, significant improvement may be seen within two weeks. Most people with psoriasis may need 15 to 20 treatments to achieve clearance and experience a remission rate of 38% after one year. For people with vitiligo, phototherapy treatment is more complex. The length of time you have had vitiligo, the body locations you want to treat and the activity of your vitiligo all influence the rate of repigmentation. Potential for response is greatest in those who have initiated treatment within 2 years of diagnosis, treat the face and neck, and who have stable, unchanged vitiligo without signs of activity. Those with signs of active vitiligo warrant more aggressive treatment often including full body phototherapy and oral steroids. Signs of activity include: Koebner phenomenon, trichrome appearance and confetti appearance.


Koebner Phenomenon is when minor trauma such as scratching triggers your condition in the location of insult.


Trichrome Appearance is where the sharp margin of pigmented and depigmented skin is blurred.  One sees a gradation of three colors instead of two distinctly contrasting colors.


Confetti Appearance is when the vitiliginous skin looks like white confetti.


But if your vitiligo is not “ideal” for treatment, that doesn’t mean you shouldn’t treat! The greatest predictor of treatment success is your motivation along with consistent combination therapy, which includes phototherapy and topical therapy.

Most people see results within 24-36 treatments, although some people respond to light therapy more slowly and changes are seen after as many as 72 treatments. Generally, patients see an average of 50-70% repigmentation of affected skin after 6 to 12 months of treatment. Areas with hair follicles, including the face, upper arms, upper legs, chest, back and buttocks, repigment the fastest and with the best results, while wrists, hands, ankles and feet are the slowest to respond. Repigmentation may be more challenging when white hairs are visible because the originating pigment-producing cells may be found in the follicle.

Why does dosage constantly change during phototherapy?

During phototherapy, your skin quickly becomes accustomed to the dose of NB-UVB energy delivered. In order for healing to continue, the dose of light delivered to targeted areas must be continually increased, depending on your skin’s response to therapy. Since everyone responds differently to phototherapy, and different areas of the body respond differently, clinicians depend on patients’ self-assessment of their skin the day after a light treatment is delivered.

With Clarify Medical™ Home Light Therapy, personalized education and careful examination of your photos helpsyou to decide whether light dosage (the length of time you treat a targeted area) should increase, decrease, or stay the same. The Clarify System automatically calculates the amount of time the NB-UVB is delivered based on your doctor’s prescription.

What happens after my skin clears?

When you reach your skin healing goals, maintenance therapy is generally recommended by your physician. Maintenance therapy involves a plan to reduce the treatment dose or frequency.  The goal here is to lengthen your time in remission, the time free of your skin condition.

If your immune system is still overactive or later becomes overactive—for example, if it’s triggered by stress, illness, trauma, childbirth, or other unpredictable or unknown causes—some degree of more active treatment may become necessary. In this case, light therapy dose and frequency is generally increased.

If you notice any changes in your condition, it’s important to discuss those changes with your doctor as soon as you’re aware of them, so you can find out what the best course of action will be to treat your skin.

And, one final note for anyone who has either experienced the ease and convenience of conducting a visit online with a dermatologist or is considering it, the Clarify System is the first at-home light therapy that can be safely prescribed online. Through Clarify’s partnership with DermatologistOnCall, we have had the chance to specially train the providers in the DermatologistOnCall network on the Clarify System. Click here to learn more.

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