A serum is a thinner formula with smaller molecules that penetrate the skin more deeply but evaporates more quickly. Because it penetrates deeply, a serum delivers its potent actives to layers beneath the outer most layer of skin.
A cream is a thicker formula with larger molecules that do not penetrate as far into the skin but provide vital protection that does not evaporate as quickly. A cream helps protect the skin, moisturizes the outer most layer, and locks in all of the good actives of the serum.
How can you use a serum and a cream together?
You can use them together by applying the serum first and then following up with the cream. The treatment potential of the serum is increased by locking in its potent actives with the heavier, hydrating formula of a cream layered on top.