Serums are formulated to deliver a very high concentration of active ingredients. Serums contain smaller molecules that can penetrate & deliver deeply into the skin.
With the smaller molecules, it allows products like ceramides and hyaluronic acid deep into the dermis. Ceramides and Hyaluronic acid help to hydrate and retain hydration deep within the inner layers of the skin (dermis) keeping healthy plump cells. Moisturiser a barrier on top of the skin surface over the serum will keep in the moisture.
There are several serums that are formulated to treat an abundance of conditions and skin types.