What's in a Scent?

Imagine a fresh-mown lawn or a recently peeled orange. Each has its own distinct smell, caused by different kinds of molecules. When inhaled, these molecules bind to specialized scent-receptor cells inside a person’s nose. The cells then send a signal to the brain, which identifies the signal as scent.

For thousands of years, people have sought to capture the smells of nature and put them in a bottle. The easiest way to do this is to extract and collect fragrant oils that occur naturally in most plants, from roses and grass to oranges. “The oils you extract from nature are a complex mixture of maybe hundreds of molecules,” says Jen Bayline. She’s a chemist at Washington & Jefferson College in Pennsylvania who teaches courses on the chemistry of perfume. “Together, they create a rich and complex fragrance.”

Once an oil is obtained, perfumers often dissolve it in alcohol. This solution can then be easily sprayed to distribute the scent.

Think of a fresh-mown lawn or a newly peeled orange. Each has a one-of-a-kind smell.  Different kinds of molecules cause each smell. Breathe in these molecules, and they bind to scent-receptor cells inside your nose. Then the cells send a signal to the brain, and the brain identifies the signal as scent.

For thousands of years, people have tried to put the smells of nature in a bottle. The easiest way to do this is to remove and collect fragrant oils. These oils are found naturally in most plants, from roses and grass to oranges. “The oils you extract from nature are a complex mixture of maybe hundreds of molecules,” says Jen Bayline. She’s a chemist at Washington & Jefferson College in Pennsylvania, and she teaches courses on the chemistry of perfume. “Together, they create a rich and complex fragrance.”

When they get the oil, perfumers often dissolve it in alcohol. Then this solution can be easily sprayed to spread the scent.

It’s a perfumer’s job to mix together both natural and synthetic ingredients to create a new, distinctive aroma. But it isn’t just a matter of choosing scents that are interesting or pleasing to smell. Perfumers also have to consider how the scents will hit a person’s nose at different times, says Anne Serrano-McClain. She owns and operates a small perfumery called MCMC Fragrances in New York City.

Every type of scent molecule has a different volatility, or tendency to evaporate. Small, lightweight molecules evaporate quickly, so a person will smell them first. Large, heavy molecules have a low volatility and take longer to evaporate. A person may smell these scents for hours after applying a perfume (see Perfumer’s Pyramid).

It’s a perfumer’s job to create new scents. Perfumers do this by mixing together natural and synthetic ingredients. But they don’t just choose scents that are interesting or pleasing to smell. They also have to know how the scents will hit a person’s nose at different times, says Anne Serrano-McClain. She owns and runs a small perfumery called MCMC Fragrances in New York City.

Every type of scent molecule has a different volatility. That means some evaporate more easily than others. Small, lightweight molecules evaporate quickly, so a person will smell them first. Large, heavy molecules have a low volatility. They take longer to evaporate. A person may smell these scents for hours after using a perfume (see Perfumer’s Pyramid). 

“The hardest part about creating perfumes is that there are endless possibilities,” says Serrano-McClain. “There are about 1,500 scents that you can choose from, but only 20 to 50 of them wind up in the bottle.”

Some perfumers want their creations to tell a story or capture a feeling. Serrano-McClain often starts with the memory of a place she has visited. A recent perfume was based on several months she lived in Kathmandu, Nepal. She wanted the perfume to evoke the scent of jasmine flowers blooming in gardens, smoke from small wood fires used in homes around her neighborhood, and burning chai tea incense.

“The hardest part about creating perfumes is that there are endless possibilities,” says Serrano-McClain. “There are about 1,500 scents that you can choose from, but only 20 to 50 of them wind up in the bottle.”

Some perfumers want their scents to tell a story or capture a feeling. Serrano-McClain often starts with the memory of a place she has visited. She based a new perfume on Kathmandu, Nepal, where she lived for several months. Jasmine flowers bloomed in the gardens. Smoke rose from small wood fires in homes around her neighborhood. People burned chai tea incense. She wanted the perfume to capture these scents.

Once she had her idea, she began experimenting by mixing together different scents that reminded her of those experiences. She started with natural jasmine and sandalwood oils, along with a synthetic scent that smells like chai. Then she complemented those scents with more than a dozen others. Once she had the ingredients figured out, she spent several weeks fine-tuning how much of each to include.

“You put the ingredients together, mix, smell it, and repeat,” says Serrano-McClain. “You just go through rounds and rounds of creating perfumes and evaluating them until you find the perfect one.”

When she had her idea, she began experimenting. She mixed together different scents that reminded her of those experiences. She started with natural jasmine and sandalwood oils, plus a synthetic scent that smells like chai. Then she added more than a dozen other scents. After she’d figured out the ingredients, she fine-tuned how much of each to include. That took several weeks.

“You put the ingredients together, mix, smell it, and repeat,” says Serrano-McClain. “You just go through rounds and rounds of creating perfumes and evaluating them until you find the perfect one.”