Vitamin D (cholecalciferol) is produced industrially by exposing 7-dehydrocholesterol to UVB and UVC light, followed by purification. The 7-dehydrocholesterol is a natural substance in fish organs, especially the liver, in wool grease (lanolin) from sheep and in some plants, like lichen (Cladonia rangiferina). Vitamin D (ergocalciferol) is produced in a similar way using ergosterol from yeast or mushrooms as a starting material.