The vitamin produced when the skin is exposed to sunlight is vitamin D. When ultraviolet (UV) rays from the sun hit the skin, a chemical reaction converts a form of cholesterol in the skin into vitamin D3, a precursor of active vitamin D. This vitamin plays a crucial role in maintaining bone health by promoting the absorption of calcium and phosphorus in the gut. Vitamin D is also important for immune function, cellular growth, and overall health. Despite its benefits, excessive sun exposure without protection can increase the risk of skin cancer.