While every step of your skin-care routine is important — no question there — they’re not all created equal. Some are more powerful than others. Face serum is one of those non-negotiable steps, in part because it can do so much for your skin.

These super-concentrated formulas target your biggest care concerns, complementing everything else you do for your skin. Yes, double-cleansing and moisturizing can do a lot in their own right, but add in face serum and you’re going to do great things for your skin — hydrate, brighten, repair, or all of the above. Here, we’re getting into exactly what is serum, along with why you need one.

What Is Serum?

A serum is a targeted treatment in your skin-care routine. It has a high concentration of active ingredients to address a particular concern, be it dehydration or dull skin. Since it addresses specific issues, you can customize the serum you use or even cocktail a few, depending on what’s happening with your skin. Serums feel lightweight and typically absorb quickly.

Serums are not to be confused with ampoules, which are also targeted treatments considered a mainstay in K-beauty. In some cases, they’re used for a limited time (think two to four weeks) in place of serum, while others are layered on before your serum step. 

How to Apply Face Serum

You should apply face serum after your toner or essence step. Why this order is especially strategic: Skin is best able to absorb ingredients when it’s damp, similar to a sponge. So, a hydrating toner like Watermelon Glow PHA+BHA Pore-Tight Toner moistens skin, ultimately allowing your serum to better penetrate. You can then follow your serum with a moisturizer to seal in all those active ingredients.

You should apply serum both morning and night, although certain ingredients are best for specific times of day. A hyaluronic acid serum, like Plum Plump Hyaluronic Acid Serum, can (and should!) be applied AM and PM. One with vitamin C, such as Guava Vitamin C Dark Spot Serum, can also be used twice a day, but you’ll get the max benefits during the daytime, since antioxidants like vitamin C serve as a backup to sunscreen, neutralizing any damaging free radicals that may sneak by. 

If you’re layering the two, follow the essential rule of skincare: Apply products from thin to thick. For that reason, we recommend applying Plum Plump — which has a thinner texture — before layering on the Guava Vitamin C serum. 

You could also mix them together before applying to your skin. Try two to three drops of Guava Vitamin C with one pump of Plum Plump — although you’re welcome to freestyle it based on what your skin needs. Keep reading for more ideas.

How to Choose the Best Serum for You

The active ingredients in a serum often play well together, which is why we’re big fans of cocktailing different serums based on what you’re looking for. That said, the best serum(s) for you largely depends on what your skin needs on any given day.

If your skin feels dry or dehydrated

To plump and replenish skin, reach for a strategic, synergistic combo of hyaluronic acid and ceramides, as in our Plum Plump Hyaluronic Serum and Avocado Ceramide Recovery Serum, respectively. There’s a difference between dry and dehydrated skin — dry skin lacks oil, whereas dehydrated skin lacks water — and the two work in tandem to deliver both. In drawing water into skin, hyaluronic acid offsets the effects of dehydrated skin, such as a slack appearance. Meanwhile, dry skin lacks the oil that’s so important to a healthy skin barrier; the ceramides, which are lipids naturally in the skin, can replenish and fortify this all-important barrier. Hyaluronic acid can help here, too, particularly in combination with emollient and occlusive ingredients that support the protective barrier.

If your skin is dull or has uneven skin tone

Vitamin C is a no-brainer for dull skin and dark spots alike. It’s one of the most powerful ingredients for brightening skin and evening out skin tone, since it suppresses an enzyme that’s integral to the pigment-production process — and no pigment, no dark spots. The Guava Vitamin C Dark Spot Serum pairs it with tranexamic acid and not one, not two, but five forms of vitamin C to inhibit pigment at a variety of checkpoints. Pair it with a niacinamide-based serum like Watermelon Glow Niacinamide Dew Drops for extra brightening power and an immediate radiance boost. Hyaluronic acid can also help here, as dry skin and dull skin are often one and the same.

If your skin is oily

Perpetually shiny skin is no match for beta hydroxy acid, or BHA, which has the ability to both counteract excess sebum and clear dead skin cells. In the Strawberry Smooth BHA + AHA Salicylic Serum, which features a blend of 2% salicylic acid alongside mandelic, azelaic acid, succinic acid, and the namesake strawberry enzymes, it can reduce oil and keep skin looking more matte.

Yet oily skin still needs hydration, as we established above. A hyaluronic acid serum will deliver lightweight moisture without adding excess oil or feeling heavy (a.k.a. the worst feeling among those with oily skin). In fact, hyaluronic acid at certain molecular weights can actually regulate excess sebum production, according to one study in the Journal of Investigative Dermatology — so you’ll get a twofold benefit of properly hydrating skin and minimizing oiliness.

If your skin is breaking out

Try using a combination of salicylic acid and vitamin C. Not only does salicylic acid’s ability to limit sebum production mean that there’s less oil to potentially clog pores — not to mention that its natural exfoliation properties keep dead skin cells from piling up — but vitamin C may also have some anti-breakout properties, too. A review of current literature published in Clinical, Cosmetic, and Investigative Dermatology analyzing the connection between air pollution and acne found that particulate matter can contribute to both inflammatory acne as well as increased sebum production, with a possible link being free radical activity. Since vitamin C smacks down free radicals, it may help in this department, too.

Keep reading about the power of serums:

• How to Combine Serums in Your Skincare Routine
• 4 Genius Ways to Make Your Serum Work Better
• Serums vs. Moisturizers: Everything You Need to Know