Fragrances are composed of many different chemicals with a wide range of molecular weights and volatilities. Not all fragrance chemicals evaporate at the same rate, so the smell varies with time. The first whiff is mostly the most volatile chemicals, which are called the “top” notes. After a short time, this fleeting aroma yields to more substantive materials, the “middle” notes. After a few hours, all that remains are the least volatile, most substantive components—the base or “bottom” notes.
A typical woman’s fragrance could have a citrus top for sparkle and instant appeal. The middle may be dominated by floral compounds. The bottom notes, sometimes called the “dry down,” can be woody, animalic and musky. Fragrances can be hard to describe and no system is perfect, but the triangle is a great start to describing the magical mix concocted by perfumers.