There are around 5000 base aromas known to perfumers, of which around 2000 are used in commercial perfumery, and less than 500 on a regular basis.

Practically all fine fragrances are constructed in layers.

• A top note layer gives the perfume accent. Top notes are relatively short-lived volatile components whose main job is provide initial impact and cover the alcohol evaporation aromas.
  
• Next comes the middle notes, the heart of the perfume. Middle notes are more enduring and are the most distinguishable character of the perfume. Middle notes are often florals or oriental/spicy smells or aromatic herbs.
  
• Finally we have base notes. These are the longest lasting elements and round the perfume off. Base notes tie the others together and can add richness, depth and warmth. Wood, moss, resins extracts are commonly used base notes.