According to Lauren Bilon, founder of Calgary-based Plume Cosmetics Inc., you can see results within a few weeks if you use serums properly. Many serums use ingredients you might find in products that help strengthen the hair on your head, such as vitamin E or vitamin B5, which work to nourish and condition the hairs. These ingredients have the same effect on brows, giving lash serums like Plume’s a dual purpose.