The skinny on skin serums

What they are

A smooth-textured serum is lighter and absorbs better than a moisturizer, penetrating deeper into the skin. "Serums usually contain higher concentrations of skin-conditioning or anti-aging ingredients compared with a day moisturizer," says Felicia Mohammed, regulatory affairs senior associate at Johnson &Johnson Inc.

Who should use them

People who want to zone in on particular skin concerns - those with uneven skin tones, age spots, fine lines or wrinkles may benefit from the use of a serum. And if you've got oily skin, the super-light formula can be a great way to add some moisture without it feeling like a coat of shellac.

How to apply serums

If you're adding a serum to your beauty routine, you don't have to trash your trusty cream - a serum can be worn alone or underneath a moisturizer. Just make sure to wait a few minutes to allow the serum to absorb first. "Using a moisturizer on top of a serum can help lock in, and increase, its cosmetic benefits," says Mohammed.

Just be careful when applying a moisturizer with retinol on top of a retinol-containing serum, or an AHA-containing moisturizer on top of an AHA-containing serum, as it may ramp up sun sensitivity.

Editor's Pick:

NEUTROGENA AGELESS INTENSIVES TONE CORRECTING CONCENTRATED SERUM, $28

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