Q: Is there a good rule of thumb for how to layer on products like serum, moisturizer, and sunscreen?
A: “In general, put on products from lightest texture to heaviest,” advises Washington D.C. dermatologist Noelle Sherber. Water-attracting hydrators like glycerin and hyaluronic acid, and active ingredients (antioxidants, peptides, or retinol) should go on first, and thicker emollients (oil, silicone, squalene) are last to seal everything in. “Water-soluble serums, especially ones with antioxidants like vitamin C or green tea need to be applied onto clean skin. Putting them on top of an oil-rich lotion limits absorption of their active ingredients.” Oil or silicone-based serum, lotion, or cream should always be applied on top of those (or be used as your sole moisturizer). “These emollients form an occlusive barrier that seals in moisture," she says, "But also prevents other ingredients from penetrating into the skin.” In the daytime, sunscreen should be your final step before makeup, so it can form a protective UV shield.