What Exactly Is A Serum?

Skin-care routines can be head-scratching enough, but if there's one product that really makes people go "huh," it's serums. The confusion mainly comes from the fact that we're told a number of products can be used as one. But, what, exactly, is a serum? "Serums are light, water-based liquids that deliver a large dose of ingredients into your skin," says Dr. Dennis Gross, creator of Dr. Dennis Gross Skincare and founder of 900 5th Dermatology. "They're truly great at delivering active ingredients to tackle your skin-care concerns." So, while your anti-aging masks and spot treatments may deliver some important elements, serums are those potent potions that feed your skin a cocktail of good-for-you ingredients.

Still, that's kind of a vague definition, especially considering the vast number of products on drugstore shelves that boast the name "serum." One main offender? Oils, which many companies claim can be used "like a serum." Dr. Gross says this isn't the case. "The difference between an oil or a moisturizer and a serum is the composition," he explains. "Serums contain no emollients, which means there is nothing to interfere with the concentrated ingredients as they reach the skin." Since most oils are emollient, they're automatically disqualified from the serums category.

Dr. Gross stresses that everyone should use a serum and that you should tailor it to your skin's needs. Folks with acne should be on the lookout for salicylic acid and willow bark extract, while ferulic acid, peptides, and glycolic acid are key for anti-aging. And, if you suffer from hyperpigmentation, a serum with vitamin C, bearberry extract, mulberry extract, and licorice root extract would be ideal.

As is typical in skin-care regimens, you should start with the lighter products, building your way to heavier ones. This means serums will typically fall immediately after washing or the second step in your routine; the only thing you'd apply before a serum would be something exfoliating — like a peel pad or an acne treatment — and a toner.

"You should apply products to cool, dry skin to ensure their effectiveness as well as decrease the chances of irritation," Dr. Gross advises. And, you should be using these guys daily. "You would be doing your skin a disservice by not using one." Well, in that case, we've rounded up five of our favorite serums. Just click ahead, find your skin type, and shop your serum soul mate.