21Lashes is easy to use and applied just like an eyeliner. Apply the serum once a day to the upper lash line – preferably in the evenings after cleansing the eye area. one brush stroke is sufficient. Allow the serum to absorb for a few moments before applying your skin care products. It takes approximately 2-4 weeks to notice the first visible results. The best results can be achieved after a 8 week treatment is completed. May cause a stinging sensation for a few of days.