What substance does human skin synthesize when exposed to UVB rays?

Human skin synthesizes Vitamin D when exposed to UVB rays. This process begins when UVB radiation from sunlight strikes the skin, converting a cholesterol derivative in the skin, specifically 7-dehydrocholesterol, into Vitamin D3 (cholecalciferol). This newly formed Vitamin D3 then undergoes further transformations in the liver and kidneys to become the active form of Vitamin D that the body can use.

Vitamin D plays a critical role in various bodily functions, particularly in calcium absorption, bone health, and immune function. The ability of skin to produce Vitamin D in response to UVB exposure highlights the importance of sunlight for human health, particularly for maintaining healthy bones and preventing diseases related to calcium deficiency.