The vitamin produced when the skin is exposed to sunlight is vitamin D. Specifically, vitamin D3, or cholecalciferol, is synthesized in the skin through a chemical reaction triggered by ultraviolet (UV) light from the sun. This vitamin plays a crucial role in maintaining bone health by aiding calcium absorption in the intestines, alongside other vital functions such as regulating the immune system. A deficiency in vitamin D can lead to health issues, including osteoporosis and weakened immunity. Therefore, safe sun exposure is often recommended to ensure adequate vitamin D production.