The vitamin primarily produced when the skin is exposed to sunlight is vitamin D. When ultraviolet (UV) rays from sunlight hit the skin, they convert a cholesterol precursor in the skin into vitamin D3 (cholecalciferol). This form of vitamin D is then metabolized by the liver and kidneys to become active vitamin D, which plays a crucial role in regulating calcium and phosphorus in the body. Vitamin D is essential for maintaining healthy bones and teeth and supports the immune system. Due to increasing indoor lifestyles and sunscreen use, many people experience deficiencies in vitamin D, making sun exposure and dietary sources important.