There are a lot of things I know I’m supposed to do before I hit 30. Invest in a 401K, find a bra that fits, get off of my parents’ phone plan, and the list goes on. One more thing to add to the list, according to board-certified dermatologist Mona Gohara, MD? Add a hyaluronic acid serum to my skin-care routine.

“Hyaluronic acid is a hydrator,” she says in a recent episode of Dear Derm. “The ingredient is naturally occurring in our skin, but when you hit about 30, you start to lose hyaluronic acid, so replacing it is a big priority for me.” Hyaluronic acid is also great for layering, because it helps your other serums penetrate more deeply into your skin, so much so that Dr. Gohara suggests putting it on before your morning antioxidant serum, like vitamin C, which is like a one-two punch of skin hydrating and brightening goodness.

Adding this extra step to your skin-care regimen doesn’t have to cost major money, either.L’Oréal Paris Revitalift Derm Intensives Hyaluronic Acid Facial Serum ($22) is made with short and long chain hyaluronic acid, which means the ingredient is able to hydrate the topmost layers of skin while also sinking deeper within skin to help plump it (bonus points for being available at the drugstore!). Dr. Gohara isn’t the only one who is totally in love with the stuff: This particular serum is so popular that a bottle of it sells every minute. At such an affordable price, you’ll have a few bucks leftover to buy that LBD. Or, ya know, invest in your 401K. Decisions, decisions.

Check out the other drugstore products Dr. Gohara swears by (not a single one of them costs more than $30!), plus the one serum she calls the “little black dress” of your skin-care routine.