Choosing a personal fragrance is not an easy task. Olfactory compositions, especially those created in artistic perfumery, are a succession of complementary raw materials skillfully combined by the perfumer to create a fragrance whose notes will develop and change over time. When we first spray the perfume, we experience the top notes; as time passes, we perceive the heart notes, and finally, after many hours, we only sense the base notes, which are more persistent.
To better understand this layering, we use the olfactory pyramid, a method that helps us visualize the composition of a fragrance, taking into account the volatility and persistence of its components. The raw materials used in an olfactory composition have different molecular weights, making them more or less diffusive and detectable at different moments. This is why we refer to them as top notes, heart notes, and base notes.
The lighter and more diffusive materials such as citrus fruits, aromatic plants, and some spices constitute the top notes as they are the first to be perceived. They bring freshness to the composition and help the essence "lift" from our skin, but they are also the least persistent. Among the heart notes, we find moderately heavy materials such as flowers, spices, and lighter woods. They are sufficiently diffusive and persistent, often becoming the centerpiece of the composition and characterizing its olfactory family. Finally, the heavier, denser, and more viscous materials like woods, resins, leather, or tobacco form the base notes of a composition. They act as fixatives, being less diffusive but highly persistent. These raw materials slow down the evaporation of a fragrance, "fixing" it and making it long-lasting.
It is important to note that we can only talk about an olfactory pyramid for fragrances made in alcohol. In oil compositions, for example, evaporation occurs much more slowly, resulting in a more linear and uniform perception of the various essences. This is also because oil has a strong affinity with human skin and remains anchored to it for a longer time.
A separate discussion is warranted for home fragrances. In this case, the olfactory pyramid does not apply because the main objective in composing an indoor fragrance is to create an essence capable of emitting a constant and single aroma. Therefore, few ingredients are used, typically two or three olfactory notes, to provide linearity and homogeneity to the composition.