Keep reading for an explainer on serums 101. How, you might ask? “Serums tend to have smaller molecules, which allow the ingredients to do deeper into the skin,” she says. So even though you may have the same active in your cleanser and moisturizer, the serum is your best bet for getting the best results from your favorite ingredients. “Serums are the workhorse products that target specific skin concerns,” Engelman says, “whereas moisturizers act as a barrier for the skin, locking in moisture.” And even though both can fix skin issues, the purpose of the serum is to address a specific issue you want to target and the moisturizer is to, well, keep the skin moisturized and healthy. But take note, Marmur says, expensive doesn’t always mean better. “Compare the ingredients of products at different price points to see the difference,” she suggests. “Less expensive products can sometimes contain less effective ingredients or a lower percentage of those ingredients,” which is something to be mindful of when choosing the best formula for you. According to board-certified dermatologist and founder of MMSkincare Ellen Marmur, M.D., skin care products should be applied from thinnest to thickest. But take note, that doesn’t include your cleanser. Your cleanser should always go first, no matter how thick or thin it is. “If you choose to use a serum, it’s usually applied after cleansing the skin and before the moisturizer,” Marmur says. Engelman agrees that thinnest to thickest is the go-to rule of thumb because it allows each layer to be fully absorbed by the skin. “If you put a serum on top of a moisturizer, the serum won’t be fully absorbed since the smaller molecules cannot penetrate the larger ones.” So, when in doubt, stick to thick creams as your last step and lightweight serums in the middle.
