This is a well known eyelashes serum that will last 3 months. It’s Sealed, unopened. 5 mL I was receiving this product through a subscription but for me the serum lasts more than 3 months! So I kept receiving them while I was still using the other one. What do I do to make it last longer with the same results? I apply the serum with the other side of the brush/applicator (see last picture) and I just use one drop for each side. I feel that I waste serum if I apply it with the brush