From the same definition it follows that the fundamental characteristic of aromatic substances is their volatile nature. For obvious reasons, non-volatile products are odorless. The volatility of the components of a perfume is not uniform, some substances are more volatile than others.

Therefore the sense of smell perceives odors in order of volatility. This important characteristic defines the cornerstone on which the framework or structure of the perfume is based. Globally, the structure is considered to be made up of three phases: top, heart and base.

Words commonly used in the definition of olfactory sensations such as "soft, ethereal, fresh, clean" refer to the most volatile fraction, and others such as "warm, dense, heavy, enduring or tenacious" are synonymous with the fraction less volatile.

The most volatile molecules are, obviously, those with the lowest molecular weight and, on the contrary, those with the highest molecular weight will always be the most tenacious, that is, the least volatile.

This physical-chemical characteristic is translated at the level of olfactory perception into sensations that, empirically, are defined with words that, although inappropriate, are the resource that best expresses the olfactory effect.