Hydration, meaning ample water content, is key to having smooth and healthy skin whether your skin is oily or dry.  Over time, the skin produces fewer glycosaminoglycans - such as hyaluronic acid - and therefore doesn't hold on to water as well and starts to show more fine lines and to lose firmness and resiliency.  There are many hydrating serums on the market, but Eve Lom's Intense Hydration Serum stands out for its pure simplicity and high quality formulation.  This absorbs immediately, and clinical studies demonstrated an increase in skin hydration of 20% in 2 hours after application.