The vitamin primarily produced when the skin is exposed to sunlight is vitamin D. Specifically, the body synthesizes vitamin D3 (cholecalciferol) when ultraviolet B (UVB) rays from the sun hit the skin. Vitamin D is crucial for maintaining healthy bones, as it helps the body absorb calcium. Adequate vitamin D levels also support the immune system and have been linked to overall health. While sunlight is a primary source, vitamin D can also be obtained from certain foods and supplements, especially in areas with limited sunlight exposure.