UVB phototherapy is used to treat a plethora of different dermatoses with a favorable side effect profile compared to systemic alternatives. One rarely mentioned issue related to phototherapy is the question of whether it holds potential to decrease folate serum levels, which is of particular interest to women of childbearing age, as birth defects, such as neural tube defects (NTD), cardiac defects, and facial clefting have all been noted to be increased in women with folate deficiency. Several studies, involving different patient groups and modes of phototherapy, have investigated the changes of folate levels throughout therapy showing mixed results. While two small open studies from Egypt showed a significant reduction of folate levels after 24 and 18 / 36 exposures (1-2), several other studies failed to show a significant change (3-6). In addition, there are also conflicting data on the influence of UVB phototherapy on vitamin D, vitamin B12 and homocysteine levels. Therefore, the presented prospective trial aims at investigating the changes of these vitamins during a routine course of phototherapy. The study will focus on the following specific aims: Measure the levels of folate as well as the levels of further vitamin parameters (including homocysteine, 25-OH-vitamin D3, 1,25-OH-vitamin D3, holotranscobalamin and methylmalonic acid) before and during phototherapy (at baseline, after 12, 24 and 36 exposures and/or at the end of treatment)