Excimer-lasers used in dermatology are so-called high-dose UV-B-therapy-gadgets.
These gadgets emit UV-B-irradiation with a wavelenght of 308nm, at very high individual single doses. Alternatively, technologies exist that apply flash-lamps (e.g. the apparatus "B-Clear®", by Lumenis®). The mode of action of these lasers and flash-lamps is comparable to conventional UV-B-therapy, however, the former generate higher individual doses and thus require fewer treatment sessions. Currently this therapy is employed for psoriasis and vitiligo.
In a normal treatment course, skin lesion are exposed to the excimer-laser or flash-lamp 3 times a week. In psoriasis at east 10 - 12 treatment-sessions are required, for vitiligo, effects can be discerned after 15 - 20 treatments. The general advantage of this new therapy is exclusive exposure of lesional skin while the healthy surrounding skin is not subjected to UV-B-rays. Especially in vitiligo this poses a great advantage as the so-called enhancement-contrast-effect (due to pigmentation (tanning) of the surrounding skin) that appears in standard irradiation treatments, does not occur. Side-effects are the same as for standard UV-B-therapy: Erythema and pigmentation of the treated skin areas, in rare cases (over-dose) formation of blisters.