A single spritz of cologne can transform you into an aromatic cloud of goodness, pleasingly triggering nearby noses for hours, if not days on end. But how do fragrances adhere so tightly to your continually-moving body for that long? The answer is actually pretty simple.
Liquid perfume is usually made from a mixture of alcohol, water and fragrance molecules that evaporate at room temperature or above. (Alcohol evaporates more quickly than water does, which helps the cologne evaporate and disperse, and having a large percentage of alcohol in the concoction spreads out the numerous different notes within so that you can distinguish them.)
When applied, the mixture binds to the natural oils on your skin — this is why people who have greasy skin may notice that their colognes last longer than those who have especially dry skin. “The molecules with odor associated with them are aromatic organic compounds (based on benzene rings) that are dissolved in a water-alcohol solution, which is then atomized into tiny droplets that diffuse through the air,” explains Alex Klotz, an assistant professor in the department of physics and astronomy at California State University, Long Beach. “If one of those droplets contacts your skin, the aromatic compounds can be dissolved in the moisture you have on your skin —from sweat, oil, etc. — and remain on the surface of your skin for a long time. If your skin is super dry and there’s no moisture, the droplets will probably evaporate, and the smellants won’t remain bound.”
Then, throughout the day, the cologne slowly evaporates into the air around you, sending fragrance molecules into your nose (and other nearby noses), where they trigger the sending of electrical signals to your brain, which then works to perceive the particular scent.
Most colognes are engineered to have a three-part smell that unfolds while they evaporate. The “top notes” normally only last for about 15 minutes and consist of odd or “spicy” smells that are meant to prompt interest without lingering for so long that they end up offending you. The “heart notes” usually last for about an hour and are composed of less pungent aromatic smells. Finally, the “base notes” typically cling stubbornly to your skin for up to six hours or so. These often have musky, watery, mossy and/or woody smells.
Because fragrance molecules in colognes adhere best to moisture and other oils, applying them directly after a shower is a good way to prolong the smell. Likewise, moisturizers provide a decent base for colognes, if you want them to last even longer.
Similarly, since fragrance molecules react to heat by evaporating and disseminating into the air, applying colognes to pulse points — like your neck and inner wrists — can help release the scent throughout the day. If you have arid skin, as Klotz mentioned, you may also find that cologne lasts longer on your clothes — where it clings to the stitching — because alcohol doesn’t evaporate from fabrics as quickly as it does from skin.
Now fly freely, my aromatic cloud of goodness. You smell great.