Procedure

Excimer Laser

A 308 nm ultraviolet B laser aimed at one patch of skin at a time. Used mainly for stubborn psoriasis plaques and for vitiligo. Because only the affected skin is treated, the rest of the body is spared the light.
Dr. Schwarz, MD · Board-certified dermatologistLast reviewed September 8, 2026
16:9 hero for Excimer Laser. Never cropped: the tone strip and the corner logo depend on the full frame.

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The excimer laser is what I reach for when someone has a few stubborn areas rather than a whole body's worth of disease — two plaques on the elbows, psoriasis along the scalp part-line, a spot of vitiligo on the cheek. It is the same ultraviolet light as a narrowband UVB cabinet, pointed at those spots only. The arithmetic is what decides whether it fits your life — two or three visits a week for two or three months, with psoriasis often thinning in the first ten to twenty sessions and vitiligo needing twenty to thirty before either of us can judge it. It is a treatment and not a cure, and it works better paired with something at home than on its own.

— Dr. Schwarz, Board Certified Dermatologist

Key Facts

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Also calledTargeted phototherapy, 308 nm excimer laser, XTRAC. The non-laser version that does the same job is an excimer lamp
DowntimeNone. The treated patch may look pink for a day
SessionsUsually 2 to 3 a week. Often 10 to 20 for a psoriasis plaque; commonly 30 or more for vitiligo
Typical costOften covered by insurance for psoriasis and vitiligo, usually after prior authorization. Self-pay is commonly in the low hundreds of dollars per session and varies widely by city
Results timelinePsoriasis plaques often thin over 4 to 8 weeks. Vitiligo needs 20 to 30 sessions before a fair judgment
PainWarmth during a few seconds of exposure. Sunburn-like soreness for a day if the dose is pushed
Skin tone safetyUsed at every skin tone. Deeper tones need a higher starting dose, and treated skin tends to tan, which can make a vitiligo patch stand out more for a while

What It Is

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A handheld device delivers a single wavelength of ultraviolet B light, 308 nm, through a small window held over the skin. The treated spot is a few square centimeters, so the light lands on the plaque or vitiligo patch and almost nowhere else. Each spot takes seconds, and a visit is usually 5 to 15 minutes. The wavelength is close to the 311 nm used in a narrowband UVB cabinet and the biology is the same. The difference is aim. A cabinet treats the whole body, right when disease is widespread; the excimer treats a defined area, right when it is not. Some offices use an excimer lamp instead: not a laser beam, same 308 nm light, same use. Because unaffected skin is not exposed, each plaque can be dosed harder than anyone would dose a whole body, which is why a course is often shorter than one in a cabinet.

How It Works

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Ultraviolet B light is absorbed by cells in the top layers of skin, including the immune cells gathered there. It pushes many of them into programmed cell death and dampens the signals they send. That is the whole mechanism, shared with narrowband UVB.

In psoriasis, immune cells are calling skin cells to divide far too fast. Removing them slows the turnover, so the scale thins and the redness settles.

In vitiligo, two things happen at once. The light calms the immune attack on pigment cells, and it prompts surviving pigment cells to multiply and move outward. Most survivors sit in hair follicles, which is why returning color appears as dots around hair openings that widen and join up, and why hairless skin such as fingertips and lips responds poorly.

Dose matters more than people expect. Too little does nothing; too much burns. Providers set the starting dose from your skin's own reaction, then raise it in small steps.

Skin is about two millimetres thick on the face. How deep a treatment reaches decides what it can change, and whether it treats all of the skin or scattered columns of it decides how long you take to heal.

How it works
Compare
Skin basics
EPIDERMISDERMISFAT0.05 mm — pigment0.5 mm — texture + pores1.0 mm — collagen1.5 mm — deep dermisPEELNEEDLINGNON-ABLATIVE LASERABLATIVE LASERSTAYS IN THE TOP LAYER

This works in the epidermis, the top layer, only about a tenth of a millimetre thick. That is the right depth for surface pigment, flaking and rough texture, and it is why nothing at this depth can change a scar or a wrinkle that is set in the layer below.

A peel or a scrub takes the skin off evenly from the surface down. Everything above the line goes and nothing below it is touched, which is why peels suit surface pigment and rough texture, and why the whole face flakes for a few days after.

Needles make hundreds of separate channels and leave the skin between them untouched. That untouched skin is what heals the rest, so recovery is quick — but a needle only injures the skin to start repair. It removes nothing.

The light passes through the surface and heats a column underneath it. The surface stays whole, so you leave red rather than raw — and it takes a course of sessions rather than one.

The laser removes columns of skin outright: the white gaps here are tissue that is gone, and new skin grows in from the sides. The strongest of the four, and the longest to heal.

The outer layer, and the only one anything in a jar reaches. It renews itself constantly: a cell made at the bottom takes about a month to reach the surface and flake off. Most of what a skincare product does, it does here.

The living layer underneath, holding the blood vessels, the nerves and the collagen. It is where lasting change happens and it is hard to reach: most of what is sold for the skin never gets this far.

What It Treats

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Vitiligo
Vitiligo
Strong evidence
The same wavelength as narrowband UVB delivered through a handpiece, so it treats one patch and leaves the skin around it alone. It suits a small number of patches, especially on the face, and it is the practical option for children who cannot stand still in a cabinet. Sessions are usually twice a week, and it is not used for widespread vitiligo.
Psoriasis
Psoriasis
Moderate evidence
Delivers the same kind of UVB light, but aimed only at the plaques, so a higher dose can be used and normal skin is spared. It suits a handful of stubborn patches, or psoriasis on the scalp, elbows and knees, rather than widespread disease. It usually takes several short sessions.
Scalp Psoriasis
Scalp Psoriasis
Moderate evidence
A focused ultraviolet beam aimed at individual patches, useful when only a few areas of scalp or hairline are involved. It treats the patch without exposing the rest of the skin. Hair blocks the beam, so it works best on the hairline and on thinner, shorter hair.
Eczema
Eczema
Moderate evidence
The same idea as the light booth, aimed at one patch instead of the whole body. Useful when a few stubborn areas are all that is left.

Not the Best For

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Alopecia Areata
Alopecia Areata
Limited evidence
Targeted ultraviolet light delivered to individual patches, usually twice a week for a few months. It is painless and can be useful for a small number of stubborn patches, including in children who cannot manage injections. The evidence is thin, regrowth often fades after treatment stops, and it asks for a lot of clinic visits.
Stretch Marks
Stretch Marks
Limited evidence
Targeted ultraviolet light used to bring color back into white marks so they blend with the skin around them. It changes the color difference, not the scar, and the effect fades over months unless it is repeated. Narrowband ultraviolet B is used the same way. It is a cosmetic option rather than a repair.

Pros and Cons

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Pros
  • Untreated skin is spared Only the patch is exposed.
  • Higher dose per spot Often fewer sessions than a cabinet.
  • Reaches awkward places Scalp part-lines, elbows, knees, small facial patches.
  • Often covered Insurance frequently pays for psoriasis and vitiligo.
  • No drug involved Nothing swallowed, nothing injected.
Cons
  • Only practical for small areas Roughly under a tenth of the body surface.
  • It is a lot of visits Two or three a week for months.
  • It fades Plaques return after treatment stops, and new color can be lost.
  • Burns are the real risk Pushing the dose too fast blisters the skin.
  • Some sites barely respond Vitiligo on the hands and feet rarely repigments.

How to Prepare

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2 weeks beforeOn the day
Sun and self-tanner
2 weeks before
No sunburn and no self-tanner on the area for 2 weeks. Both change how much light reaches the skin and make the dose unreliable.
Clean skin and scale
On the day
Come with the area clean, with no makeup or thick creams. With thick psoriasis scale, some providers ask for a thin film of mineral oil, since scale scatters light.
For vitiligo
Expect photographs at the start and every couple of months. Slow repigmentation is hard to judge from memory.

What Happens

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ArrivingThe treatmentLeaving
Arriving
The area is looked at and often photographed. The provider checks what has changed since last time — sunburn, new medicines, soreness after the last session. Nothing is numbed. Your provider will ask about these things.
The treatment
You and the operator wear ultraviolet goggles. The handpiece goes over the patch and light comes in bursts of a few seconds per spot. No smell, no noise beyond the machine, no feeling beyond mild warmth. Doses are written down each visit so the next can be adjusted. If the dose was too high you feel it hours later, like a small sunburn.
Leaving
Straight back to work. The treated squares may look faintly pink.

Recovery

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Day 1 to 2After several sessionsAfter weeks
Day 1 to 2
Tenderness, deeper redness or mild peeling means the dose ran ahead of what your skin tolerated. Report it — the next dose should be lowered, not raised.
After several sessions
Treated skin darkens. The outline of the treatment window can show for weeks, which surprises people. It fades.
After weeks
Psoriasis plaques flatten and shed less. Vitiligo shows pinpoint dots of color, or a narrowing edge, long before the patch looks even.

Aftercare

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Same dayEvery day
Makeup and sun
Same day
Makeup once you leave. Keep the treated area covered or shaded that day and use sunscreen on exposed skin — the dose assumed no extra ultraviolet on top of it.
Moisturizer
Every day
A bland moisturizer daily. Dry, scaly skin transmits light unevenly.
Actives
Do not start a new retinoid or acid on the treated spot mid-course without saying so. It changes how the skin reacts.
Report a burn
Tell the office before the next visit if the area blistered or stayed sore more than a day.

Risks

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Most of what happens is expected and mild: warmth, pink skin, tanning of the treated squares, and dryness. Risk rises when doses are raised quickly, and when something else has made the skin light-sensitive.

A burn
Soreness, deep redness, or blistering a day after a session. The dose needs lowering, not repeating.
A cold sore
Ultraviolet light can set one off on the face. Antiviral treatment works best started early.
Dark patches
New darkening at the edge of the treated area, most often on deeper skin tones. It usually fades. Flag it early rather than at the end of the course.
A new medicine
Any new prescription started mid-course; some make the same dose behave like a much bigger one.
Long term
Ultraviolet exposure carries a theoretical skin cancer risk. Studies of narrowband UVB have not shown a clear increase, and the excimer exposes far less skin than a cabinet. Keep a record of your sessions.

In Deeper Skin Tones

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This is one of the better options for vitiligo at deeper skin tones, and it is used at every tone. Dosing is the important part.

Deeper skin tones tolerate a higher dose before burning, so the starting dose is higher. Providers set it from a test dose or from your history of burning, both better than guessing from appearance. Starting too low wastes months; starting too high burns.

Expect two pigment effects. Treated skin tans, so a slightly darker square can outline where the device was placed. Around a vitiligo patch that tanning increases the contrast for a while, making the patch look more obvious partway through a course, before the color returning inside it catches up. Both settle.

Dark patches from a burn: The outcome to avoid, because they last longer at deeper skin tones. If the area is sore or blistered after a session, say so before the next one.

If You Stop

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There is nothing to taper and no withdrawal. Stopping removes the light.

Psoriasis plaques usually come back, most often over weeks to a few months, though the clear stretch varies a lot between people. That is the disease returning, not a rebound from stopping.

Vitiligo is different. Color that has come back often stays, particularly on the face and particularly if the disease is quiet. It can be lost again while the vitiligo is active, which is why providers keep a topical going after the light stops. Repeating a course later usually works about as well as the first.

Combining Treatments

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Same day
Psoriasis creams
Topical steroids and vitamin D creams such as calcipotriene pair well.
Same day
Psoriasis medicines
It can continue alongside methotrexate, acitretin or a biologic.
Same day
Vitiligo creams
Tacrolimus or ruxolitinib cream is a common pairing, and beats light alone in studies.
Same day
Moisturizer
Between sessions it helps light reach the skin evenly.
Wait 2 weeks
Peels, laser, waxing
Do not treat skin that has just been peeled, lasered, waxed or sunburned.
Ask your doctor
Light-sensitive medicines
Tell the office if a new medicine makes skin light-sensitive.
Don’t combine
Tanning beds
Avoid them during a course; the extra ultraviolet is not counted in your dose.

Insurance Coverage

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Insurance in the US often covers targeted phototherapy for psoriasis and vitiligo, usually after prior authorization and often only once topical treatment has been tried. Coverage for vitiligo used to be refused as cosmetic more often than it is now, and appeals with photographs and a letter from the dermatologist are frequently successful.

Self-pay pricing is usually in the low hundreds of dollars per session, depending on the size of the area, the city, and whether the office sells a package. Billing is per session and courses run to dozens of sessions, so the number that matters is your copay multiplied by the number of visits.

Ask Your Doctor

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If you are pregnant or breastfeeding
Ask the doctor managing your pregnancy or breastfeeding before starting.
If you take a light-sensitizing medicine
Doxycycline, some diuretics, some antifungals, St John's wort. The same dose can burn.
If you have lupus or porphyria
Or another light-sensitive condition. Ultraviolet treatment may be the wrong choice.
If you have had melanoma
Or many skin cancers. Weigh this against your history first.
If you take immune-suppressing medicine
It changes both the skin cancer discussion and the plan.
If the area is more than a tenth of you
A whole-body cabinet is usually more practical. Ask which one you are being offered.
If your vitiligo is spreading right now
Active disease often needs calming first, and light alone may not hold the ground.
If you have a deeper skin tone
Ask how the starting dose will be set, and whether a test dose is being used.
If a session leaves the area sore
Or blistered. Say so before the next appointment.

At-Home Versions

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Home narrowband UVB cabinets and panels
Good alternative
Full-size or half-size units prescribed for home use, with the dosing schedule set by the dermatologist. The main route for people who cannot get to an office two or three times a week. Needs a prescription, insurance work, and discipline about the log.
Handheld narrowband UVB wands
Okay alternative
Combs too. Small 311 nm devices for scalp and limited patches. Closest thing at home to what the excimer does in the office, at a lower dose per second, so sessions run longer.
There is no home 308 nm excimer
Bad alternative
Excimer devices are office equipment. Anything sold online under that name is something else, usually a low-power light with no dosing control.
Sunlight
Okay alternative
Deliberate sun exposure helps some people with psoriasis and vitiligo, but the dose is uncontrolled, it exposes skin that does not need treating, and burns set both conditions back. Discuss it rather than improvising it.
Tanning beds
Bad alternative
Wrong spectrum, uncontrolled dose, whole body, and the clearest skin cancer risk of anything on this list.

How It Compares

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Narrowband UVB cabinet
Different job
The same biology delivered to the whole body, which is the better choice once disease is widespread. The trade is that unaffected skin gets the ultraviolet too, doses per session are lower, and courses tend to run longer.
Topical steroids and vitamin D creams
Different job
Cheap, done at home, and the first step for limited psoriasis. Slower on thick plaques, and long unbroken use of strong steroids thins skin, which is one reason light is added.
Topical calcineurin and ruxolitinib
Different job
Creams for vitiligo. Strong evidence for ruxolitinib cream, moderate for tacrolimus. Used at home, no visits, and combining them with light works better than either alone in studies. Cost and insurance approval are the obstacles.
Biologics and systemic drugs
Different job
For psoriasis. Strong evidence. Far better for widespread or joint disease. For two plaques on the elbows, most people would rather not take a systemic drug, which is exactly the gap the excimer fills.
PUVA
Worse
Largely superseded. A drug plus ultraviolet A, with more side effects, strict eye protection afterward, and a clearer long-term skin cancer signal than narrowband UVB.
Surgical grafting for stable vitiligo
Different job
For patches that will not repigment with light and have been stable for a year or more. A procedure rather than a course, done by a small number of centers.

Finding a Provider

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This is dermatology office equipment. The treatment is usually delivered by a trained nurse or medical assistant working to a protocol the dermatologist sets, which is normal and fine.

Worth asking: how the starting dose is chosen, whether they use a test dose, whether doses are logged every visit, how many sessions before you both review, and what they do if an area burns. For vitiligo, ask whether they photograph and how often.

Red flags: no goggles for you or the operator, no written record of dose, a promise of cure or a set percentage of repigmentation, pressure to buy a long package before a test dose, and offices selling targeted ultraviolet as general skin rejuvenation.

Myths

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  • "It is a laser, so it burns the plaque off." It removes nothing. No cutting, no heat damage, no resurfacing. It delivers ultraviolet light and the skin does the rest.
  • "One or two sessions should show something." They will not. This is a course measured in weeks for psoriasis and months for vitiligo.
  • "It cures psoriasis or vitiligo." Neither. It clears or repigments while it is being used and for a variable stretch afterward. Both conditions can return.
  • "A tanning bed does the same job for less." Tanning beds emit mostly a different part of the ultraviolet spectrum, at uncontrolled doses, over the whole body. They carry the skin cancer risk this treatment is designed to limit.
  • "Vitiligo cannot be treated at deeper skin tones." It can. Targeted phototherapy is used at every skin tone, with a higher starting dose and an experienced provider.

Questions Patients Ask

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How is this different from a narrowband UVB cabinet?

Only in where the light goes; the wavelength and biology are the same. The excimer treats defined patches at a higher dose each and leaves the rest untouched, which suits limited disease. A cabinet treats everything at once, which suits widespread disease.

Does it hurt?

Not much — a few seconds of warmth per spot. If the dose was pushed too far you feel it hours later, like a small sunburn.

How many sessions before I know if it is working?

For psoriasis, roughly 10 to 20. For vitiligo, 20 to 30 before judging at all. Stopping earlier is the most common reason people conclude it did not work for them.

Will the results last?

Nobody can promise that. Psoriasis plaques usually return after treatment stops. Vitiligo repigmentation often holds, especially on the face and when the disease is quiet, and is more likely to be lost while it is still active.

Is it safe on deeper skin tones?

It is used at every skin tone. The starting dose is higher, treated skin tends to tan, and the outcome to avoid is a burn, since dark marks from a burn last longer at deeper skin tones.

Does it cause skin cancer?

Ultraviolet exposure carries a theoretical long-term risk. Studies of narrowband UVB have not shown a clear increase, and the excimer exposes a fraction of the skin a cabinet does. Keep a record of your sessions and mention it at skin checks.

References

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