The extra air between the sun and the shore
At the Dead Sea, the shoreline sits hundreds of metres below the average level of the ocean. Sunlight therefore travels through a slightly deeper column of air before reaching a person there than it would at sea level. Air molecules and tiny particles scatter some sunlight, while gases in the atmosphere absorb particular wavelengths. That leaves a little less ultraviolet radiation at the surface.
The effect is not a shield. Sunburn is driven especially by UVB, and the atmosphere’s ozone layer absorbs much of it long before sunlight reaches the ground. The extra air near the Dead Sea filters only an additional fraction. How quickly skin burns still depends on the sun’s angle, cloud cover, time outdoors, and a person’s skin—not simply the elevation of the shoreline.
Reflected light still reaches you
The region’s bright, open surroundings matter too. Sunlight reflected off water or pale ground can reach skin from below or from the side, including places a hat’s shadow does not cover. That makes the Dead Sea’s unusual elevation an interesting part of its setting, not a reason to treat the shore as sunburn-proof: the extra atmosphere may reduce exposure somewhat, but direct and reflected UV can still accumulate during a visit.
