According to photothermolysis, the FPDL(flashlamp-pumped pulsed dye laser) treatment theoretically causes no epidermal damage, however, we have observed blister, crust and scars in clinical experiences, and we have also found that FPDL has limited effect on adults, specially, thick-skinned Asian people with rich melanin pigmen. In order to explain these effects, we took biopsies and made a histologic observation and analyzed the results statistically.
  The biopsies were taken from 15 patients who received first treatment and stained with H&E and NBTC(nitroblue tetrazolium chloride). We measured epidermal melanin content, epidermal damage, vessel wall coagulation depth, RBC coagulation depth, mean vessel diameter and evaluated clinical results at post-treatment 6 weeks.
  The vessel diameter and darkness of lesion color were incrased with ages. Complete vessel coagulation was restricted to small vessels. With increasing epidermal melanin content, epidermal damage increased accordingly. The clinical results were enhanced with increasing coagulation depth of vessel walls, and deteriorated with increasing epidermal melanin content. The clinical result was not significantly correlated with RBC-coagulation depth or energy used.
  We observed that melanin pigments have an adverse effect on clinical results. The FPDL treatment can be a choice of treatment to children with light colored lesion, but has a limitation to Asian adults with rich melanin pigment. Therefore, repetitive treatment is necessary for improvement of clinical results.