The Dead Sea is unique. It is 1300ft below sea level and due to the high mineral content has a constant haze overhead. Because it is the lowest place on earth the atmosphere is very thick, the haze and the additional atmosphere, create a natural ultraviolet light filter unlike that of the surrounding area or anywhere else on earth..
This natural filter blocks many of the shorter UVB intense "burning" rays while allowing the longer UVB wavelengths to pass though to the skin. Some of these longer wavelengths are what may be called " narrowband" they are in the 312-318 nm wavelength range and have been found to effectively destroy tcells as they have the energy of the shorter wavelengths but the penetration of the longer wavelengths
Additionally, this intense sunlight creates two or more types of Vitamin D...high test or calcitriol in the skin and D3 or cholecalciferol which we make up to 20,000iu/day and is converted by the liver to calcidiol and raising ones blood levels of Vitamin D. Both help to control the tcell activity via VDR's or vitamin D receptors on the cell.
This combination of geography and unique atmospheric conditions at the Dead Sea has proven to be a successful for many people. The remissions vary from weeks to months and depend on a variety of factors..length of stay, time of year, individual differences etc.
