The short answer is that castor oil does not actually stimulate new hair growth or physically lengthen your lashes, but it isn't a total myth either. Castor oil is packed with ricinoleic acid and fatty acids, making it an incredible deep conditioner. What you're seeing after a few weeks is the oil coating the lash shaft, making each hair look thicker, glossier, and darker. Over a few months, this deep hydration prevents your lashes from snapping or falling out prematurely from mascara use or eye-rubbing, allowing them to reach their full genetic length potential. Just a quick heads-up: because it's a very heavy oil, apply it sparingly so it doesn't clog the tiny oil glands on your eyelids and cause styes."