Serums are formulated to deliver a very high concentration of active ingredients. Serums contain smaller molecules. Therefore the tiny molecules allow serums to penetrate & deliver deeply into the skin.
Smaller molecules allow products like ceramides and hyaluronic acid to penetrate deep into the dermis. Ceramides and Hyaluronic acid help hydrate. They retain hydration deep within the inner layers of the skin dermis. Therefore keeping healther skin cells.
Moisturiser, a barrier on top of the skin surface over the serum, will keep in the moisture.
Several serums are formulated to treat an abundance of conditions and skin types.