Phototherapy

A cabinet or panel of lamps emitting ultraviolet B in a narrow band around 311 to 313 nanometers. You undress to the treated areas, put on goggles, and a timer runs the exposure. The dose starts low — set from your skin type or a test of how much light turns your skin slightly pink — and climbs each visit. Smaller versions handle smaller problems: panels, wands, units for hands and feet, and combs that part the hair to reach the scalp. The excimer light or laser at 308 nanometers treats small stubborn patches at higher doses without exposing the rest of your skin. A dermatologist prescribes it; trained staff run the sessions from a written protocol.

Ultraviolet B is absorbed in the top layers of skin and does not reach the rest of your body. In psoriasis and eczema it damages the DNA of overactive immune cells there badly enough that they die off, and it quiets the inflammatory signals they send. In psoriasis it also slows the runaway production of skin cells, which lets plaques flatten. In vitiligo it calms the immune attack on pigment cells and pushes the survivors sheltering in hair follicles to multiply and spread outward. That is why repigmentation starts as freckle-like dots around individual hairs, and why fingertips and lips respond so poorly. The narrow band at 311 nanometers keeps the benefit while cutting the shorter wavelengths that mainly cause burning.

Narrowband UVB is used across all skin tones and is a mainstay for vitiligo in all of them. Three practical differences matter.

Dosing starts higher and courses run longer. Melanin absorbs ultraviolet, which is the point of it, so more light is needed for the same effect, and deeper skin tones typically need more sessions to clear psoriasis or eczema.

Redness is harder to see, so burns get missed. The dose climbs based on whether the skin went pink, and that signal is much less obvious here, which puts the weight on what you report. If the skin felt hot, tight, tender or itchy after a session, say so before the next one even if nothing looked red. That habit is the best protection against a burn, and a burn is what leaves lasting dark patches.

Contrast changes during vitiligo treatment. Treated skin tans, so the pale patches can look more obvious partway through a course before they fill in. Temporary, and better to hear in advance. Repigmentation works across all skin tones, with the same pattern everywhere: face and neck best, hands and feet worst.

Stopping does not cause a rebound, but it does not hold the result either. Psoriasis usually returns over weeks to months, and the gap varies enormously — a few weeks for some people, more than a year for others. Eczema behaves the same. So some people go onto a reduced maintenance schedule instead of stopping, and some repeat courses seasonally, often through winter. Vitiligo is the exception: regained pigment is often kept, though it can be lost if the condition is still active, which is why topical treatment usually continues. The light treats what is happening, not why.

This is one of the few treatments here that insurance often pays for, because it treats a medical condition. Coverage for psoriasis, eczema and vitiligo is common in the US, usually with a copay per visit. The catch is arithmetic: at two or three visits a week for two or three months, even a modest copay becomes a large total, before parking and time off work. Ask the office to work out the likely total with you at the start.

Home units are often cheaper over a full course, an argument insurers sometimes accept. Handheld units cost least, panels sit in the middle, full-body cabinets run several thousand dollars. Prior authorization takes weeks, so start the paperwork early.

Excimer laser for small patches is priced per session and less consistently covered, so check first.

Narrowband UVB is given in dermatology offices and hospital units by trained nurses or technicians following a dermatologist's written protocol. Machines need periodic calibration — an aged lamp delivers less light than the setting says. Worth asking: Is this narrowband UVB at 311 nanometers, not UVA or a tanning device? How is my starting dose decided? Who adjusts it if I burn? Is a record kept of my cumulative sessions? Will you prescribe a home unit if the schedule becomes impossible? Red flags: a tanning salon or spa advertising phototherapy, no goggles, no record of doses, no dermatologist supervising, and a refusal to say when the lamps were last measured.

• "A tanning bed is the same thing." It is not. Tanning beds emit mostly ultraviolet A with a little UVB, not the narrow band around 311 nanometers that does the work. The dose is not set for a medical purpose, nobody tracks it, there is no shielding, and the cancer risk from commercial tanning is well established. Dermatologists have used it where no phototherapy is within reach, but that is a reluctant compromise.
• "It is just getting a tan." Tanning is a side effect, not the mechanism. The treatment acts on immune cells in the skin and, in vitiligo, on pigment cells in hair follicles.
• "Phototherapy gives you skin cancer." The evidence differs by treatment. PUVA, the older tablet-plus-UVA combination, raises risk at high cumulative doses. Narrowband UVB studies have not shown a clear increase, though long-term data are limited. That is why sessions are counted and skin checks continue.
• "It cures psoriasis." It clears the skin. The underlying condition is unchanged, and psoriasis generally returns over weeks to months.
• "Home units are unsupervised and unsafe." A prescribed unit uses the same lamps, the same dosing protocol and the same eye protection, with a dermatologist setting the schedule and reviewing progress. It is not a machine bought online.
• "Missing a couple of weeks makes no difference." It does. Skin loses the tolerance it built, so the dose steps back down after a gap. Pushing straight back to the old dose is a common cause of burns.

1. Carrascosa JM, Ubogui J, Gilaberte Y, et al. Narrowband UVB Phototherapy in Dermatology: GEF-CILAD 2026 Update. Actas dermo-sifiliograficas. 2026. — Actas dermo-sifiliograficas, 2026
2. Wu YH, Chou CL, Chang HC. Risk of skin cancer after ultraviolet phototherapy in patients with vitiligo: a systematic review and meta-analysis. Clinical and experimental dermatology. 2022. — Clinical and experimental dermatology, 2022
3. Home Narrowband Ultraviolet B Phototherapy for Photoresponsive Skin Conditions: A Health Technology Assessment. Ontario health technology assessment series. 2020. — Ontario health technology assessment series, 2020
4. Drucker AM, Zhong Y, Tomlinson G, et al. Narrowband versus broadband ultraviolet B phototherapy for adults with moderate-to-severe atopic dermatitis: a randomized controlled trial. The British journal of dermatology. 2026. — The British journal of dermatology, 2026
5. Kirke SM, Lowder S, Lloyd JJ, et al. A randomized comparison of selective broadband UVB and narrowband UVB in the treatment of psoriasis. The Journal of investigative dermatology. 2007. — The Journal of investigative dermatology, 2007
6. Sezer E, Etikan I. Local narrowband UVB phototherapy vs. local PUVA in the treatment of chronic hand eczema. Photodermatology, photoimmunology & photomedicine. 2007. — Photodermatology, photoimmunology & photomedicine, 2007