The terms "top notes", "middle notes", and "base notes" used in perfumery are frequently a source of confusion because they cause a great deal of misunderstanding in modern perfumery. These terms were much simpler when perfumers used to create perfumes with a classic pyramid structure, at a time when they didn't use large quantities of "linear" aroma chemicals as they do today.
Three layers of notes
First Impression
These are the scent components you notice first when you apply the perfume. They are the most volatile, meaning they evaporate the fastest.
The Heart of the Perfume
These are the main character that emerges after the top notes fade, and can still be felt hours later.
Lingering Trail
These are the least volatile notes that remain on the skin during the perfume's dry-down phase.
The pyramid model and its limitations
These descriptions are often visualized alongside a pyramid diagram, which can be somewhat misleading because it's not actually how we smell a fragrance. A pyramid gives the impression that each material flows in order from top to bottom — when in reality, this is not the case.
In reality, at the beginning of the fragrance, you will mostly detect top notes, some middle notes, and some base notes. Then, middle and base notes come to the forefront more; finally, only base notes remain — this is what is called the dry-down phase of the perfume.
While the fragrance pyramid is a useful marketing tool, it's not very helpful for perfumery students and can lead to great confusion.
Flexibility and linearity
Some flexibility is required when classifying perfumery materials as top, middle, or base notes; therefore, it should be used as a loose guideline rather than a strict structure. Materials interact with each other, and some top notes can slow down, while base notes can elevate themselves more than they would on their own.
Today, the fragrance structure in commercial perfumery is becoming more linear and is often characterized by the overuse of very high-impact aroma chemicals; therefore, the notes you first perceive may not necessarily be the top notes.
