What Does Serum Do, Exactly?

Adobe Stock

In the world of skin care, "serum" is part of the standard vocabulary — but if you're just dipping your toe in, you might be wondering what a serum even is, let alone how you're supposed to use one. If you've been struggling with your skin and can't seem to get past a certain skin concern, serums, however, could be just what you need.

"Serums are a class of skin-care products designed to deliver high concentrations of a particular active ingredient to the skin," says dermatologist Joshua Zeichner, M.D. Essentially, in a well-rounded skin-care routine, a serum is considered the "treatment" step. This is thanks to higher concentrations of active ingredients and their often thin texture, which makes them ideal for layering. There are serums that feel as runny as water and serums that feel more like light lotions — but most of the time, you'll find that they sit somewhere right in the middle of that spectrum. Packaging also varies, from pipettes (the dropper caps seen on many serums) to pumps.

Where does serum go in your skin-care routine? First, you cleanse to wash away makeup and dirt and, of course, make sure you're applying products to a clean canvas. Then, it's serum time. "Because they tend to have a lighter consistency, serums can be layered underneath your other skin-care products," adds Zeichner. (Fun fact: a good rule of thumb for the order in which you apply your skin-care products is to move from those with the thinnest consistencies to the thickest.) Moisturizers are typically heavier than serums and also contain occlusive ingredients that work to lock in moisture and thus also prevent other ingredients from soaking into the skin. That's why it's best to use serums underneath these thicker products. If you have a more maximalist routine, your order might look something like cleanser, toner or "essence," serum, moisturizing cream, and sunscreen in that order, explains dermatologist Dan Belkin, M.D.

When looking for a serum, the key is to pick an ingredient that speaks to your particular skin goals or concerns. "Not all serums are created equal, and your best friend's favorite serum may be different than what is right for you," notes Dr. Zeichner. Though a serum is not absolutely mandatory the way SPF is, dermatologists agree that most people can benefit from one chosen to match their skin concerns.

Take note: Once you start using a new serum, it might take some time to see results. "With the exception of hyaluronic acid, which can give almost instant plumping hydrating benefits, most ingredients in serums need several weeks to months to truly exert their effects," says Dr. Zeichner.

Finally, you don't want to overload your skin with active ingredients, so make sure to look at your skin-care routine holistically (consulting a board-certified dermatologist is definitely helpful here) to make sure you're not overdoing it. For example, chemical exfoliants like glycolic acid (an alpha hydroxy acid) don't mix well with retinol, another strong ingredient, and can lead to irritation when combined. (See: 4 Signs You're Using Too Many Skin-Care Products)

Now that you finally have the answer to "what is a serum" and what a serum does, here's how you can join the club. Here, dermatologists share the ingredients to look for in a serum, depending on your skin's needs — and of course, the best serums for your skin.

Dry Skin

"Those with dry skin should look for serums with humectant ingredients such as hyaluronic acid, which draws in moisture like a sponge," notes dermatologist Onyeka Obioha, M.D. Lactic acid and honey are also effective humectants, notes Dr. Belkin.

Try It: Peter Thomas Roth's Water Drench Hyaluronic Glow Serum (Buy It, $68, sephora.com) or The Ordinary's Lactic Acid 10% HA (Buy It, $7, sephora.com), which blends both hydrating ingredients (for under $7!).

shp - 7 Available at Sephora

Dark Spots & Brightening

For brightening, Obioha recommends focusing on "pigment-reducing ingredients such as vitamin C, niacinamide, and alpha arbutin." Vitamin C is a constant when it comes to dermatologist favorites. "This potent antioxidant not only protects your skin from free radical damage but also blocks production of abnormal pigmentation," explains Dr. Zeichner. (FYI, using antioxidants is one of the most important steps of preventing aging and protecting your skin against environmental damage.)

Try It: Saint Jane's CBD-infused The C-Drops (Buy It, $90, sephora.com) has a powerful dose (20 percent!) of the star ingredient. Naturium's Alpha Arbutin Serum 2% (Buy It, $20, amazon.com) blends the namesake ingredient with niacinamide.

shp - 90 Available at Sephora

Acne

The hero ingredient for acne is salicylic acid (also known as a BHA, or beta hydroxy acid) which is a chemical exfoliant that gets deep into the pores and helps unclog them. You can find it in products like Caudalie's Vinopure Natural Salicylic Acid Pore Minimizing Serum (Buy It, $49, sephora.com).

However, Dr. Belkin adds that ingredients like "niacinamide, zinc, retinol, and glycolic acid," can also help, explaining that niacinamide (aka vitamin B3) "can reduce sebum production, which can be a problem in acne, and thereby the appearance of pores," zinc can be "anti-inflammatory and help reduce redness in acne," and retinol (aka vitamin A) is "a hugely important molecule for the skin that can create healthy skin turnover and prevent the formation of comedones (aka clogged pores)." Finally, glycolic acid is a gentle chemical exfoliant that can "remove dead skin cells and help prevent pores from becoming stuck," which is what occurs with acne.

Try It: Peace Out's Salicylic Acid Treatment Serum Treatment Serum (Buy It, $34, sephora.com) blends salicylic acid and niacinamide while Drunk Elephant's T.L.C. Framboos Glycolic Resurfacing Night Serum (Buy It, $90, sephora.com) combines BHAs with AHAs (like glycolic acid).

shp - 90 Available at Sephora

Redness & Irritation

For redness-prone skin, look for ingredients that soothe and calm the skin. Obioha recommends "colloidal oatmeal and ceramides, and thermal spring water." Ceramides help repair the skin's barrier and oatmeal is super soothing and hydrating for the skin.

Try It: Aveeno's oat-fortified Aveeno Calm Restore Triple Oat Serum (Buy It, $18, amazon.com), which combines oat flour, oil, and extract to help restore a compromised skin barrier, or Kate Somerville's ceramide-enriched DeliKate Recovery Serum (Buy It, $85, katesomerville.com), or Avene's Hydrance Intense Rehydrating Serum (Buy It, $38, dermstore.com).

shp - 85 Available at Kate Somerville

Lines & Wrinkles

Unsurprisingly, Dr. Zeichner's pick for aging skin is retinol. "It is perhaps the best-studied anti-aging ingredient we have on the market," he explains. "It stimulates collagen production to strengthen the foundation of the skin and reduce the appearance of fine lines and wrinkles." (More options here: The Best Retinol Product for Every Skin Type)

Try It: Alpha H Vitamin A Serum with 0.5% Retinol (Buy It, $55, sephora.com) or L'Oréal's Revitalift Derm Intensives 0.3% Pure Retinol (Buy It, $37, ulta.com).

shp - 55 Available at Sephora