The excimer laser produces ultraviolet light at 308 nanometres, right next to the 311 nanometres used in a narrowband UVB cabinet. Biologically it is doing the same job: quieting the overactive immune cells that drive psoriasis, and prompting surviving pigment cells to move back into a vitiligo patch. The difference is delivery. A handpiece is held over the patch, so the light lands on affected skin and nowhere else.
That targeting is the whole point. Doses in a whole-body cabinet are limited by the most sensitive skin in the booth, since the same light hits your treated patches and your healthy skin alike. When only the plaque is being treated, a much stronger dose can be used safely, and stronger doses clear plaques in fewer visits. It also means your unaffected skin collects no ultraviolet exposure at all over a course, which matters more the more courses you have over a lifetime.
Bring a full list of your medicines and supplements. Anything that makes your skin sensitive to light changes the dose.
Expect a test dose at the first visit. The provider treats a small area or several small test spots at different settings, then reads the result a day later to set your starting dose. Skipping this step is how blisters happen.
Do not apply creams, ointments or sunscreen to the patch beforehand unless your clinic asks you to.
Some clinics apply a thin layer of mineral oil to thick, scaly plaques just before treating, which helps light penetrate. Follow their instruction.
Say something if a treated area blistered after the previous session. The dose should come down rather than continue upward.
You sit or lie down, and the provider marks or identifies the patches being treated.
You wear protective goggles. Everyone in the room does.
The handpiece is held against or just above the patch. Each pulse takes a few seconds. A small plaque may be a single placement; a larger one is covered in overlapping spots.
You feel warmth, sometimes a mild snap. It is not usually described as painful.
Most appointments run five to fifteen minutes depending on how many patches are being treated, and much of that is set-up.
The treated patches often look slightly pink straight afterwards. That is expected.
There is no recovery period and no restrictions. You go back to work or the gym immediately.
Pinkness in the treated patch for a few hours to a day is normal, and is a sign the dose is in range.
Blistering is not normal at a well-chosen dose, but it is more common with the excimer laser than with a cabinet, because the doses are higher. A small blister usually heals without a mark in a few days — report it so the next dose is reduced.
Treated patches may end up slightly darker than the skin around them during a course. This settles over weeks to months after you finish.
Keep the area moisturised between sessions, but not in the hour before one.
Psoriasis: plaques usually start flattening after four to six sessions, and many people clear a treated patch in 10 to 15 sessions. This is meaningfully faster than a cabinet for the same plaque, because the dose per session is higher.
Vitiligo: slower. The first dots of colour typically appear after 20 to 30 sessions. The face responds best, and often quite well. Hands, feet, elbows and lips respond poorly regardless of how long you continue — if those are your main areas, the excimer laser will probably disappoint you.
How long it lasts: a cleared psoriasis plaque commonly stays clear for three to six months, sometimes longer. It usually returns in the same spot, and a repeat course generally works again. Repigmented vitiligo is often more stable than that, though some patches fade over the following years.
Stretch marks are a separate case. The excimer laser can bring colour back into pale marks so they blend in, but the colour fades over months and needs repeating. It changes the colour, not the texture or the indentation, and it is rarely a first suggestion for that reason.
There is no home version of an excimer laser. The devices are expensive medical lasers and are not sold for home use.
The closest home equivalent is a handheld narrowband UVB wand, which a dermatologist can prescribe. It uses a slightly different wavelength at a lower dose, so it needs more sessions, but it treats the same kinds of small areas and you do it at home on your own schedule. For someone with two stubborn plaques and a long drive to the clinic, that is often the more practical option.
A tanning bed is not a substitute for either. It delivers mostly UVA over your whole body with no dosing and a well-established cancer risk, which is the opposite of the argument for targeted treatment.