Nature has been splashing itself with eau de this-is-my-territory-not-yours and guess-what-I'm-in-heat cologne spray for a long time. You have to wonder who made that leap to scraping the secretions from the anal gland of a civet cat into a perfume bottle, but somebody did. Someone also emptied the scent pods of male musk deer into a bottle of fragrance. That was the source of original musk. In, too, went the stuff inside the urine and scent sacs of beavers and the intestines of sperm whales.
Although they were popular in early perfumes, few fragrances contain real civet, musk, castoreum or ambergris anymore. It's now cheaper and easier to synthesize imitations in the lab, and affordable modern perfumes usually go that route.
Modern perfumes have progressed to fouler-smelling compounds. Take Eau de Stilton, which radiates blue cheese, a Stilton Cheesemakers Association commission meant to turn more stomachs on to the product [source: Discover]. You could say the Stilton fragrance was a joke, but real perfumes sometimes boast notes of stench as a sort of circus act by the designer, too. Luca Turin, a biophysicist and well-known perfume writer, thought the rotten note in Sécrétions Magnifiques, considered a fine fragrance, was thrilling and intelligent [source: Turin and Sanchez].
To apply the loosest definition, perfume is any substance that you wear and that smells. There are no requirements for it to smell good. Clearly, your experience of a perfume comes not only from the stuff in the bottle but also from the stuff in your head. Read on to learn what's in the bottle.
What Is Perfume?
In liquid perfume, the liquid is a mixture of alcohol, water and molecules that evaporates at room temperature. "A smell is basically a molecule that's light enough to float in the air, although not every molecule that's light enough to float in the air has a smell -- carbon monoxide, for example," says Avery Gilbert, a sensory psychologist who has consulted for the fragrance industry. What creates the fragrance is that cells in your nose recognize the evaporating molecules and send electrical messages to your brain, which creates a perception. To learn exactly how we smell, read How Smell Works.
If you've read the French phrases on your perfume bottle, you may know that perfumes come in different strengths. The most concentrated are perfume oils. They have been pressed out, steamed out or chemically separated out of a plant, flower or fruit [source: Sell]. In perfume oil, fragrance molecules are dissolved in 98 percent alcohol and 2 percent water. Everything else is alcohol-diluted perfume oil. From most to least concentrated, parfum is at least 25 percent perfume oil; eau de parfum is 15 to 18 percent; eau de toilette is 10 percent; and eaux de cologne and body spray are lighter [source: Turin and Sanchez].
The perfume world also classifies perfumes into scent families. The categories exist because critics and designers use the terms. There are no groupings that everyone agrees on, nor any rule about categorization beyond common sense and a perfume belonging if it smells like the last perfume in the category. Here are some classifications you may have encountered:
- Floral: smells like flowers
- Fruity: smells like fruit, including citrus
- Green: fresh grass or leaves
- Herbaceous: like any variety of herbs
- Woody: like different types of wood
- Amber: like tree resin
- Animalic: bodily smells
- Musk: like a substance made by the musk deer
- Oriental: amber and spice
[source: Turin and Sanchez]
Sometimes perfumes are categorized according to the structure of one of its fragrant molecules:
- Aldehydic: fatty but makes other smells radiate
- Lactonic: creamy and fruity
- Phenolic: smells like tar
Tired of these subjective categories? There are no ambiguities in the chemistry of perfume, except in the secret ingredients, of course. Read on to learn basic perfume chemistry.
Why is perfume so diluted? It's not that manufacturers are stingy. The reason is actually aesthetic: Lots of alcohol spreads out the smells so that you can distinguish them. In a perfume oil, you'd encounter a jumble of smells. Smelling it would be like hearing an orchestra play all the notes in a symphony at once. You might register that you're smelling something sweet, but not that it's mango, followed by jasmine, finished with cherry. Its diluted nature makes the smell enjoyable.
In fact, most perfumes are engineered to have a three-part smell, which unfolds after you apply it to your skin. You smell top notes within the first 15 minutes of applying. These chemicals first evaporate off your skin. Designers often put weird, unpleasant or spicy smells in this phase so that they interest you but don't hang around long enough to offend. Heart notes appear after 3 to 4 hours. The chemicals creating these smells evaporate more slowly from your skin. They're probably what you remember about the perfume; if it's a floral perfume, flowery smells go here. Base notes stick stubbornly to your skin. You smell them within 5 to 8 hours of application [source: Sell]. Musky, watery, mossy and woody chemicals often go in the base [source: Calkin]. The word note is just perfume jargon for an individual smell.
Knowing that perfumes smell by evaporating, you can take better care in applying them. When applying, spread the perfume, but don't rub it in vigorously, because the heat you create will evaporate the top notes and weaken the overall smell.
Chemical reactions can also morph your perfume on the shelf. Visible light has enough energy to bust the bonds in fragrance molecules, and bright sun will singe your perfume in as little as a week [source: Turin and Sanchez]. Air can also corrode your fragrance by oxidation -- the same process that turns uncorked wine into vinegar. Storing your perfume at room temperature, in the dark and in a spray bottle preserves it well. Then, it will have a shelf life of at least two years [source: Sell].
But what about your chemistry? Your temperature and oiliness seem most important. The top notes will evaporate faster from warm and dry skin than cool and oily skin. Otherwise, by the time the heart notes emerge, the perfume smells the same on everyone [source: Turin and Sanchez].
You have learned about your perfume's structure and behavior. You have spread, but not rubbed vigorously. Next, we'll look at how the fragrance industry produces the stuff.
Launching a New Perfume: From Brief to Buying
Perfume production starts with a company's plan to sell you a perfume. Let's say Gucci wants to launch a new fragrance. The company will write a description called a brief. It explains who the perfume should appeal to and why, plus what the scent should say to the smeller, such as "classy," "irreverent" or "sunrise in Thailand." It explains what forms the fragrance will take -- a light green spray and a white soap, for instance -- which helps chemists choose compatible ingredients. Finally, it explains where and for how long the products will be sold: in Europe and Asia for the next two years.
The brief gets mailed to several fragrance houses. Fragrance houses are companies that run two operations. They employ perfumers, who design and write the formulas for perfumes. Fragrance houses also stockpile thousands of perfume ingredients: spices held in warehouses; fruit and flower oils; and vials of chemicals that approximate cigar smoke, leather or endangered types of wood. Chemists support both operations. Fragrance houses employ analytical chemists who can pinpoint the molecules in an unknown liquid using an analytical technique called gas chromatography mass spectrometry (GCMS). Fragrance houses also employ synthetic chemists who can build those molecules.
The perfumer reads the brief, thinking about what smells are in a Thai sunrise. She writes a list: lime, coconut rind, papaya and chili pepper. Next, she considers sources. Coconut rind might be in the perfume house's warehouse. If the company doesn't own the smell of fresh papaya, it will have to buy the product of someone's headspace effort, which we'll talk about in a second. The company would also need to make or buy a chemical that smells like chili pepper, since real extract would burn the nose.
You may wonder how fragrance houses maintain their caches. They may buy ingredients from farmers then milk out the juices by steam distillation or chemical extraction. They could also buy from firms that do the legwork. But since fresh and steamed papaya emit different smells, they may use a method called headspace. A fragrance house affiliate would put a ripe Thai papaya in a jar and essentially vacuum out the smell for up to eight hours [source: Sell]. The samples would go back to the fragrance house, where a chemist would analyze the sample by GC-MS, getting a printout of the molecules in that smell. She would try to synthesize the smell from scratch.
Launching a New Perfume: Mixing It Up and Dousing the Public
Once the ingredients for the proposed perfume are assembled, the next step is mixing. The perfumer writes instructions for mixing the smells in different ratios, which technicians do in company labs [source: Turin]. One version might smell mostly like coconut, while another might be heavier in chili-lime. By choosing chemicals with different evaporation rates, the perfumer can control what you smell first, second and so on. Does a Thai sunrise smell like papaya, then pepper, or does the morning start out spicy?
The perfume house makes 10 to 100 versions of the perfume, which specialists smell and screen [source: Turin]. The best go to Gucci.
Gucci smells the attempts of the fragrance houses and dismisses those it thinks have missed the point of a Thai sunrise. From the rest, it asks for modifications, perhaps liking version No. 3, but finding the coconut too sweet.
The fragrance houses rework their perfumes. They swap in ingredients that are maximally economical, long lasting and safe. They test on skin, trying to maintain the smell's shape: If the perfume smells of fruit, then spice, ghost notes of fruit should remain even as the spice is taking over. The perfume may need three chemicals for the fruit smell -- one to evaporate quickly, one to stay longer and one to hang on for dear life [source: Sell]. The perfume houses test on consumers, comparing ratings for their perfume to a top-selling perfume. The numbers and the perfume go to Gucci.
Gucci chooses a fragrance and one lucky perfume house wins a contract. The winner sells the fragrance concentrate to Gucci at an agreed-upon price until the perfume goes out of production. The perfume house sends the concentrate to Gucci in up to 1-ton drums (0.9 metric tons) [source: Sell]. No one but the perfumer and her colleagues knows the exact formula, not even Gucci.
Chanel No. 5: A "Natural" Choice?
Why do we wear perfume at all? Men and women do it for different reasons, says Rachel Herz, a psychologist at Brown University who studies the psychology of smell and author of "The Scent of Desire: Discovering our Enigmatic Sense of Smell." Young men do it to attract women. Older men do it out of gratitude to the women who gave them the perfume.
For women, the reasons also depend on age. Women in their twenties are inspired by the media -- a singer or movie star -- and by their friends. Women in their 30s follow no particular pattern. By 40, women wear fragrance simply because they like it. And by 60, women think mostly of other people's wishes, wearing perfume because a daughter, spouse or friend likes it, according to Herz's research.
But why Chanel No. 5 and not Coco? The question of why we choose one perfume over another is complex, hotly pursued by the fragrance industry and tied up in scientific debate.
Here's what's clear: People don't like smells that are physically irritating. Chemicals like ammonia, for instance, burn when you smell them. The effect happens because the molecules activate a pain system in the face.
Although it's speculative, your choice may depend on your calibration to the intensity of certain smells, which depends on your genetically determined number of odor receptors. Odor receptors on cells in your nose grab fragrant molecules from the air. With more receptors for a class of compounds -- let's say, lily smells -- you may smell lily at a lower concentration, but at normal amounts, the smell could be intense and overwhelming. "In general, things that are high-intensity tend to be aversive," says Herz. "You may love a certain symphony, but if someone plays it really loud, it will be unpleasant."
Having few receptors for an odor could also foul your opinion of a perfume. Cilantro's fragrance consists of many odors. If your genetic code spells out a variation that reduces your number of receptors for an odor, you may miss one of cilantro's odors, and it may smell soapy and foul, says Gilbert. With a different genetic variation and the average number of receptors, cilantro may smell herbal and refreshing. "It's like color filters on a lens," says Gilbert.
Evolution Leading Us by the Nose?
To what extent are our smell preferences programmed? Here's where psychologists like Gilbert and Herz take opposite olfactory stands.
According to Gilbert, there are categories of smells that most people like and dislike. Our predispositions are explained by our evolutionary history, he says. We like fruity and floral smells because "plants make fruit aroma to attract seed dispersers," and we once ate fruit to live, says Gilbert. "The apple says, 'I smell good. Eat me. Spread my seeds all over the place.'" And we did. Flowers appeal because plants use the same building blocks to make chemicals that attract pollinators and seed dispersers, Gilbert says.
We dislike fecal, urinous, fishy and rotten odors because historically "it meant you and your primate friends were hanging around the one sleeping tree too long, and it was time to move to a clean one. There's a connection between those kind of odors and disease, bacteria, viruses." So perhaps only the ancestor who was adverse to those smells survived to pass on the alleles.
Herz, however, asserts that there are no such predispositions, at least none that cultural or personal experience can't overwrite. Infants, she points out, don't display innate scent preferences and are indifferent to the smells that adults in their culture like and dislike. Cultures also disagree on what smells bad. She points to a U.S. Army study that could not find a stink-bomb smell disliked by a range of ethnic groups [source: Herz]. Latrine smells don't bother people who grow up with them, and rotten meat was tolerated and even liked in Europe before the days of refrigeration [source: Herz]. "The reason people like any fragrance has to do with learning," she says.
As a silly twist, marketing affects the choice, too. A confusing message, such as a perfume pitched as romantic but smelling more like metal, can cause buyers to put down a smell they otherwise like.
Memory, Mood and Attraction
If your favorite perfume reminds you of your mother, you're not alone. "Women often wear fragrances within the same categories as their mothers did," says Herz. "This tends to be because of the positive association, and because smelling someone's perfume is an evocative cue for being brought back to that person."
And if you wear perfume to make others remember you, you and some companies think alike. Westin Hotels, for instance, fans white tea smells into the lobby, hoping you'll remember this dimension of its logo [source: Westin].
Can a perfume change your mood? There's no scientific research on perfumes, but studies have examined individual smells. Gilbert points to a study in which pleasant food smells seemed to make people nicer. In a mall, an actor dropped a pen or asked for change either near Cinnabon, a cinnamon roll retailer, or out of smelling range. "With the Cinnabon odors in the air, people around the area were more helpful to strangers and in a better mood. The effects are small and brief, but they're real," says Gilbert.
The claim that perfume can boost your sex appeal certainly makes money for the fragrance industry. "There is absolutely no evidence that there are aphrodisiac compounds out there," says Herz. However, if you believe that your perfume makes you more attractive, you're more likely to behave confidently or flirtatiously, which could make you seem more appealing, she adds.
We do judge potential mates based on smell -- often, on body odors that we can't control. "People tend to mate nonrandomly, picking people who have different genes for the immune system," specifically the major histocompatibility complex, says Gilbert. "The inference is that we're doing it based on a smell. No one has identified the molecule that is the product of this immune gene. People might not even be aware [of the smell]."
This hasn't stopped the marketing of purported "pheromone perfumes" that claim to contain come-hither ingredients, like steroid derivates. What these do for the wearer and smeller isn't clear.
"In cases where mating pheromones work, like in pigs, the animals have an accessory olfactory system, a tubelike structure in the nose called the vomeronasal organ (VNO) that is specialized for picking up these molecules, and there is a specialized set of nerves for transferring information to the brain," says Gilbert. As for a human VNO, he adds, "Some people say we have it. Some people say we don't. Others say it might be a vestigial organ like our appendix, where we have it but it doesn't work."
"The commercial marketing relies on the assumption that our response is going to be like the pig response -- that the woman in the bar is going to start salivating all over you," says Gilbert. "Yeah, right."
Related HowStuffWorks Articles
More Great Links
- "The Secret of Scent" by Luca Turin
- "Perfumes: the Guide" by Tania Sanchez and Luca Turin
- "The Scent of Desire: Discovering Our Enigmatic Scent of Smell" by Rachel Herz
- "What the Nose Knows: the Science of Scent in Everyday Life" by Avery Gilbert
- New York Times: "Varying Sweat Scents are Noted by Women" by Nicholas Bakalar
- Bakalar, Nicholas. "Varying Sweat Scents are Noted by Women." The New York Times. Feb. 17, 2009. (Feb. 17, 2009) http://www.nytimes.com/2009/02/17/health/17swea.html?_r=3
- Calkin, Robert and J. Stephen Jellinek. "Perfumery: Practice and Principles." John Wiley & Sons. 1994.
- Discover Magazine. "Eau de Stilton." Cosmic Variance Blog. May 12, 2006. (Feb. 17, 2009)http://blogs.discovermagazine.com/cosmicvariance/2006/05/12/eau-de-stilton/
- Gilbert, Avery. Personal interview. Conducted Feb. 17, 2009.
- Gilbert, Avery. "What the Nose Knows: the Science of Scent in Everyday Life." Random House. 2008.
- Herz, Rachel. Personal interview. Conducted Feb. 20, 2009.
- Herz, Rachel. "The Scent of Desire: Discovering Our Enigmatic Scent of Smell." HarperCollins. 2007.
- Sell, Charles, ed. "The Chemistry of Fragrances: from Perfumer to Consumer." Cambridge: Royal Society of Chemistry. 2006.
- Turin, Luca. "The Secret of Scent." HarperCollins. 2006.
- Turin, Luca and Tania Sanchez. "Perfumes: the Guide." Penguin Group. 2008
- Westin Hotels. "Westin Hotels launches signature home fragrance collection." Sept. 20, 2006. (Feb. 27, 2009) http://www.starwoodhotels.com/westin/about/news/news_release_detail.html?obj_id=0900c7b980642a5f