Where does this hyaluronic acid serum fit in my routine, and can I use it under moisturizer?

Yes — applying this serum before your moisturizer is the ideal layering approach and significantly enhances the performance of whatever you put on top. Apply it to clean, slightly damp skin immediately after cleansing or toning, before any creams or heavier products. Hyaluronic acid works by drawing moisture from the environment and keeping it “trapped” against the skin’s surface — applying it to damp skin gives it more water to work with, and sealing it in with a moisturizer on top prevents that moisture from evaporating. You can apply it morning and evening, and the directions also allow for additional midday application on particularly dry or dehydrated days. Under sunscreen in the morning is also an effective use.