الفهرس 
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Abstract
Psoriasis is a common chronic skin disease, affecting approximately 2% of the world population.
Psoriasis is considered as an autoimmune disease that is triggered by an activated cellular immune system involving innate and adaptive mechanisms. Clinically and histologically, psoriasis has a well characterized appearance.
The exact etiology of psoriasis has not yet been completely understood. The evolving evidence suggests that psoriasis is a complex disorder caused by the interaction of multiple genes, the immune system and environmental factors.
Treatment options for psoriasis include topical treatments, oral treatments, phototherapy and biologics, optimizing and tailoring the therapy for psoriatic patients is essential and dependent on severity of the disease.
Ultraviolet (UV) spectrum is divided into UVC (100–280 nm), UVB (280–315 nm) and UVA (315–400 nm). UVB penetrates into papillary area of the dermis inducing DNA damage of resident dendritic cells and keratinocytes inducing apoptosis upon UVB radiation.
The aim of the current study is to assess the effect of NB-UVB phototherapy on serum folate levels in patients with chronic plaque psoriasis in comparison to healthy normal individuals.
The study was conducted on thirty Patients of both genders with chronic plaque psoriasis and thirty age and sex matched healthy normal controls.
The group of Psoriatic patients included 16 males (53.3%) and 14 females (46.7%), while control group included 15 males (50%) and 15 females (50%). there was no statistically significant difference between the two groups regarding sex. (P=0.796).
Duration of the disease ranged from 1.0-15.0 with the mean of 7.53 ± 3.99 years