The Dead Sea's Unique

about 330 sunny days annually,

high barometric pressure, i.e., around 5% greater in the winter and more than 3% during the summer, relative to the that at sea level as a result of it being the lowest terrestrial site on Earth,

a higher density of air than any other terrestrial site on the earth as a result of its high barometric pressure, viz., more oxygen molecules per unit volume

the erythema irradiation (the lowest wavelengths within the UVB irradiation range, that causes sunburn and other deleterious effects such as skin cancer), is attenuated by selective filtration as a result of the relatively longer optical path length the solar rays must traverse to reach the lowest terrestrial site on Earth