BACKGROUND: The process of making that perfect perfume requires a unique marriage of science and art. Science brings various techniques to the union that isolate the individual scents: cold-press processes, distillation, extraction, or making synthetic molecules, for example. Fragrance artists known as "noses" make the more subjective judgment calls to combine those components into a beautiful scent.
WHAT IS PERFUME: Perfume is a mixture of fragrant essential oils and aroma compounds, fixatives and solvents that give off a pleasant smell. Perfumery began in ancient Egypt and was further refined by the Romans and Arabs. Perfumery also existed in East Asia, but most of those fragrances were based on incense. A mixture of alcohol and water is used as the solvent for isolated aromatics. On application, body heat causes the solvent to quickly disperse, leaving the fragrance to evaporate gradually over several hours.
TAKING NOTES: There are three basic components, or "notes," in perfume. Top notes are scents that can be detected immediately when the perfume is applied; they form that critical "first impression." Citrus and ginger are common top notes. Heart notes (middle notes) describe the scent that emerges after the top notes dissipate, usually 2 minutes to one 1 hour after application. They form the main body of a perfume. Lavender and rose are often used as middle notes. Base notes -- such as musk and plant resins -- also appear after the top notes have disappeared, serving as fixatives to hold and boost the strength of the lighter top and heart notes.
THE NOSE KNOWS. Experts known as "noses" are responsible for combining the various "notes" into the full composition of a perfume. Noses must have a keen knowledge of a wide range of fragrance ingredients and their smells, and to be able to tell the difference between them, whether alone or in combination. Such experts are extremely rare.
HOW WE SMELL: A smell is the sensory response to the complex mixtures of chemicals in the air around us, called odorants. We are able to sense these chemicals because they bind to protein receptors that line the cells in our nose. Each kind of receptor can only detect specific chemical compositions, producing the sensation of different smells. These receptor proteins are produced from about 1,000 different genes: almost 3 percent of our total gene count.