الفهرس 
Ultraviolet Radiation (UVR) and SkinOnly 14 pages are availabe for public view
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Abstract
The human skin is exposed to a wide spectrum of electromagnetic radiations including UV, visible and infrared radiations. UVR is a specific type of the wide electromagnetic radiation spectrum that includes the wavelengths between 200 - 400nm in the form of three bands: UVA, UVB and UVC.
Melanin is well-known as the major defense of the skin against the hazardous effects of UVR.
In the current research, we assumed that the epidermis plays a complex photoprotective role beyond that of melanin. Photoprotective mechanisms of the epidermis include physical factors and naturally occurring epidermal agents. Physical factors include SC and/or viable epidermal thickness. Naturally occurring epidermal agents may include several solar UVR-absorbing epidermal chromophores such as DNA, UCA, aminoacids, and others. Such choromophores are distributed within epidermal layers in varying concentrations and correlate with SPTs.
This study comprised 48 subjects ranging in age from 7 to 58 yrs; they were subdivided into two groups; group I which included 24 patients with vitiligo with SPT II, III, IV and V, group II which included 24 normal volunteers with SPT II, III, IV and V and served as a control. Both groups were age and sex-matched.
All participants were subjected to SPT determination by “Fitzpatrick self-reported” questionnaire, Stripping of SC of vitiliginous and normal skin, (in cases and controls) and BB-UVB phototesting for MED.
The study included 4 skin models; vitiliginous, stripped vitiliginous, normal, and stripped normal skin models. Consequently, epidermal components; SC, melanin, and VE were calculated.
Statistical analysis of results revealed that there were a linear relationship between MED and SPT in different skin models of group II, this may be secondary to epidermal chromophores or other factors that increase with increasing SPT. However, this was not found in stripped and non stripped normal skin models in group I, which may be due to previous therapeutic UVR exposure, which may have a long term impact on vitiliginous patients.
There was a difference between stripped and non stripped areas due to the effect of SC. The difference between vitiligo and normal areas is secondary to absence or presence of melanin.
Differences between VE, melanin and SC revealed that VE has the major role in photoprotection followed by SC and then melanin. Interestingly, no correlation was found between SPT and MED in SC and melanin. This finding requires further research.
We conclude that the photoprotective role of the epidermis beyond that of melanin is as important as that of melanin. This role was shown not to be constant but active in relation to internal and external factors. The physical factor through epidermal layers thickness plays a role but the biological factor based on active epidermal chromophores may have the leading value in this process. Further studies of these factors may provide a new base for future photoprotective therapies.