If you’re going to choose a single skin-care product to shell out for, pros agree that it should be your serum. These products deliver the most highly concentrated active ingredients and are meant to serve as the treatment step in your routine—which means they’re giving you more bang for your buck than your cleanser or moisturizer.

But if you’re dropping $100 for a three-ounce formula, you’ll want to ensure you’re getting the most out of it… otherwise, you’re more or less wasting your money. The best way to do that, according to celebrity esthetician Gina Mari? By avoiding one of these common mistakes.

1. Forgetting to exfoliate

Exfoliating is important for getting rid of the dead skin cells on the surface of your skin. Not only does the process help to brighten your complexion, though, it also makes it easier for your serums to penetrate more easily. “Exfoliating the skin prior will allow for deeper product penetration,” says Mari. Keep in mind that you don’t need to exfoliate every day, though—integrate this step into your routine two to three times a week and you should be good to go.

2. Applying in the wrong order

In order to get the most out of your serum, you’ll want to position it properly in your routine. According to Mari, you should start with your cleanser, then exfoliate if needed, then tone, then apply your serum. This process will ensure that your complexion is prepped and ready for whatever actives you apply so that they can really get down deep into your pores. Once you’ve put on your treatment, Mari suggests waiting for five to 10 minutes to let it seep into your skin, then seal it in with a moisturizer.

3. Rubbing instead of patting

It can be tempting to slap some serum into your hands and rub it all over your face, but when you do that, you run the risk of wasting product because much of it winds up on your hands instead of your face. Instead, pump some product onto your fingertips and press it into your skin. “When applying serum, always apply in an upward motion and avoid rubbing and tugging the skin,” says Mari. She adds that this pressing motion will help with product penetration, so you’ll get more results with less product.

4. Mixing ingredients

With skin care, more doesn’t necessarily mean better. When you’re using multiple serums, you run the risk of combining ingredients that might cancel each other out or cause irritation, like retinol and vitamin C. “Be cautious of layering too many different products—pick one and allow it to do its job,” says Mari. If you want a serum that delivers multiple different benefits, look for a formula that’s already done the mixing for you. “There are many serums on the market that have the perfect blend of actives, therefore leaving the guesswork out of the equation,” says Mari.

Shop serums

Alpha-H Liquid Gold Exfoliating Treatment with Glycolic acid — $54.00

Get that oh-so-important exfoliating step in with this AHA-packed serum. It’s made with glycolic acid and lives up to its “liquid gold” moniker by melting away dead skin cells to help totally resurface your skin.

Biossance Squalane + 10% Vitamin C Dark Spot Serum — $62.00

Derms say everyone should be using a vitamin C serum as part of their a.m. routine, and this one serves double duty by both brightening skin and fading the appearance of dark spots. It pairs the hero antioxidant with complexion-nourishing squalane, which means it’ll also give you a solid dose of hydration.

Sunday Riley A+ High-Dose Retinol Serum — $85.00

Replace the dead, dull skin cells on the surface of your complexion with this do-it-all retinol serum, which stimulates cell turnover while you sleep. The result is smoother, brighter skin with fewer wrinkles, dark spots, and breakouts.

For more tips on how to properly use vitamin C serum—aka the “little black dress” of your routine—check out the video below.

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