A scent is not a snapshot but a progression. What you smell at the first sniff is rarely what lingers hours later. In perfumery, that progression is described with a classic model: the fragrance pyramid, with a top, a heart and a base. Once you know it, you understand why a scent lives on the skin.
What the fragrance pyramid is
The fragrance pyramid is a common model in perfumery that divides a scent into three layers that come forward one after another. You smell the top note first, the heart note follows, and the base note lingers longest. It is not a strict law but a useful way to describe how scent molecules evaporate at different speeds. Light, volatile molecules rise quickly, heavy molecules cling to the skin longer.
Top, heart and base
The top note is the first impression, often fresh or citrusy, and usually disappears within a quarter of an hour. The heart note forms the actual character of the scent and unfolds in the minutes and hours that follow. That is the scent you carry through the day. The base note consists of the heaviest molecules, often woody or warm, and determines what still echoes in the evening. Together the three layers give a scent its progression and its depth.
Why a scent smells different on your skin
A scent behaves differently on the skin than on a paper blotter. Your skin temperature, your natural sebum and even your diet influence how the layers unfold. That is why the same beard oil never smells exactly alike on two men. It is also why we test our scents on the skin and not only on blotter. A scent that convinces on paper has to prove itself again on the skin. That is how we build our beard oil.
A good scent does not show its true nature in a second, but over the course of a day.