Pheromones are airborne, mostly odorless chemicals that alter sexual behavior, mark territory, and influence reproduction throughout the animal kingdom. But whether humans send and receive "sex chemicals" is a hot and bothered topic.
Recent tantalizing studies suggest that chemicals emanating from our pores do affect the behavior and biochemistry of others. Fragrance companies have caught whiff of this research, and the Internet abounds with products sporting names such as "Primal Instinct" or "Rogue Male" promising to make you an irresistible sex magnet.
The real warning about human pheromones should be "buyer beware." While many scientists believe that human pheromones exist, they disagree about whether they have identified any specific chemical compound that is one. In the popular understanding, pheromones cause an instinctual, almost automatic sexual response, which scientists call a "releaser" effect. That effect is well-studied in animals, but has never been observed in humans.
Nevertheless, fragrance companies are focusing -- and funding -- research concerning pheromones' potential for sexual arousal. "There's often a sexual component in the way we sell our fragrances," said Leslie Smith, an organic chemist and vice president of fragrance technology development at Coty International. "Can we put something into our products that can generate the pheromone effect and enhance attraction? We know that animals have signaling chemicals that induce sexual behaviors."
For example, a male pig secretes the pheromone androstenone in his saliva, and when the female "smells" it, she goes into a mating stance. "The dream of male humans is that there would be such a compound," joked Carol Christensen, a psychologist in the research division of International Fragrance and Flavors.
If humans do produce pheromones, the underarm is where we might do so, with its many glands and its proximity to a companion's nose. Our sebaceous glands secrete a clear liquid that becomes mixed with thousands of odorless compounds oozing from other glands. Bacteria on our skin break down those compounds into volatile molecules, both odoriferous and odorless, producing an "odor print" as unique as our fingerprints. Any pheromones among them would drift into our companion's nasal passage and stimulate specialized but still elusive receptors. Finding those receptors will resolve the dispute about whether humans have a "vomeronasal organ" devoted to sensing pheromones, as many other animals do, or whether pheromone receptors are interspersed with olfactory receptors in the nasal passage.
George Preti, an organic chemist at the Monell Chemical Senses Center in Philadelphia, first began sniffing out the secrets of the underarm in the 1980s in collaboration with Winnefred Cutler of the University of Pennsylvania's psychology department. They hoped to explain the observation that women living together fall into menstrual synchrony, having their periods at the same time, a finding made in 1971 by Martha McClintock, a leading pheromone researcher now at the University of Chicago. Preti and Cutler discovered that women exposed to just the underarm extracts of other women adjusted their menstrual cycles to be in synch, and that male underarm extracts made women with irregular cycles more regular.
They hypothesized that those underarm extracts must contain pheromones, because the effects could not be explained in any other way, and they were consistent with the way pheromones function in other mammals. Since then, other researchers have followed the underarm trail. Recently, Preti and his Monell colleague, Charles Wycoski, reported that male underarm extracts can affect the cycles of a specific reproductive hormone in women. Those extracts also affected the mood of women, making them calmer and more relaxed.
What about the effects of female pheromones on men? In a 2001 study conducted by researchers at the University of Texas, men described the smell of a woman's T-shirt as more "sexy" or "pleasant" during the fertile stage of her menstrual cycle than the shirt of the same woman during her infertile stage.
But which molecules in the underarm secretions are active pheromones? Some researchers -- who often tend to market pheromone products -- claim to know, but most maintain that it's still a mystery. "It's a big challenge to separate, identify, and rebuild these chemicals," explained Smith.
Two compounds that gained a mixed reputation as pheromones are androstadienone (AND) and estratetraenol (EST). AND is a derivative of testosterone and EST is a poorly understood relative of estrogen. Synthesized versions of these compounds have been patented and Christensen, of International Fragrance and Flavors, suspects some companies license them to market as sexual "essences," but that information would be a trade secret.
Could AND and EST be human pheromones? Some scientists are ready to say yes, because the chemicals change brain patterns as detected by EEGs, functional MRIs, and PET scans, and induce mood changes. That evidence is consistent with what pheromones would do, said Christensen. However, Preti disagrees: "Those results were obtained from solutions of pure compounds with a thousand times the concentration found in humans."
Meanwhile, Preti's former collaborator, Cutler, claims to have found the key to sexual attraction using a different set of compounds. She reexamined data from their 1986 studies and noticed that the women wearing the presumed female pheromones reported more frequent sexual activity than those wearing a placebo. She hypothesized that something in that extract acted as a sexual attractant. She claims to have synthesized the female and male sexual essence, which she markets through her for-profit Athena Institute and advertises in magazines. Users mix these odorless elixirs, which cost $100 for a sixth of an ounce, with their perfume or cologne. To provide legitimacy to skeptics, Cutler subjected her proprietary products to independent, double-blind, placebo-controlled studies; however, she did not reveal the chemical composition of the ingredients to the researchers. The results? "The stuff works," said Norma McCoy, a professor of psychology at San Francisco State University, who conducted the study in young women in 2000. Seventy-four percent of those using the product perceived an increase in intimate activity involving a male, compared with 23 percent who used the placebo.
These studies, however, did not examine physiological or biochemical changes. And critics contend that the data did not support those conclusions. They point to inconsistencies with the numbers and to the small sample sizes and short time period of the studies. "But the biggest problem is that the experiment can't be replicated because we don't know [the chemical composition of] what was being tested," said Preti. "Scientists have trouble with secrecy."
Controversy aside, Christensen said pheromone research is reshaping the fragrance industry, indicating that the romance of scent is not just the fragrance you put on your skin, but also the chemicals that are coming out of your pores.
So what's a lovelorn person to do? Remember that should pheromones actually make you more attractive, it's probably just a fleeting first impression; then your other charms, or lack of them, take over. When a man asked Christensen if he should buy a pheromone product to increase his sex appeal, her advice was, "Don't stop brushing your teeth."
© Copyright 2003 Globe Newspaper Company.