How (and Why) to Use Face Serum

It's a beauty misconception that serums are just a more expensive form of skin moisturiser. Yes, the price is more per ounce than your average skin care product, but that's because you're getting more concentrated ingredients (and deeper-penetrating effects). Get the low-down on why serums are worth every penny when you keep reading.
Why use it? A serum is your go-to product to improve the overall look of your complexion. The active ingredient can bring antioxidants to the skin, restore cell growth, or help decrease pore size. But the one thing a serum doesn't do, typically, is moisturise the skin.
How does it work? "Moisturisers have a base that allows them to stay on the surface to moisturise the outer portion of the skin, but a serum has a lipid-soluble base that allows the active ingredient to actually penetrate into the epidermis," explains Dr. Lawrence Samuels, chief of dermatology at St. Luke's Hospital and founder of the skincare line in the US.
Which one is right for you? "If you have acne-prone skin, the two most significant ingredients would be an L-ascorbic acid [which is true vitamin C] and retinol," Dr. Samuels says. "They're both antioxidants that improve the cell growth in the outer layer of skin." If you have normal skin, look for alpha lipoic and glycolic acids in the serum ingredient list.

How do you apply it? Use about a pea-sized amount of serum for the face and neck, applying the product about two minutes after your cleanser (not on wet skin). "Hydrated cells allow the active ingredient to penetrate better than dried cells," Dr. Samuels says. Then, wait another three to five minutes before applying your moisturiser. "Moisturisers help restore the keratin protein back to the skin, so they generally have a higher pH," he said. "If you put on your serum then immediately put on your moisturiser, it can somewhat decrease the effectiveness of your serum."
Also, it's important to use face serums primarily at night, because UV rays and oxygen can cause them to oxidise — another reason to make sure you always keep a tight lid on your products.