Lumisterol is a vitamin D precursor that is synthesized in the skin when exposed to UV radiation. Lumisterol is a naturally occurring compound that is found in human skin, as well as in some plant and animal sources. Lumisterol impurities are unwanted substances that can be present in lumisterol preparations, which can affect the potency and purity of the final product. It is important to carefully identify and remove these impurities to ensure that lumisterol preparations are safe and effective for use.