Pheromones: No Love Potion No. 9 Despite those ads on the Internet, there is no firm evidence that humans emit or respond to pheromones. Scientists coined the term "pheromone" 50 years ago this month when they were able to identify a chemical sex signal between silkworms.

Pheromones: No Love Potion No. 9

Pheromones: No Love Potion No. 9

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The first chemical identification of a pheromone involved Bombyx Mori silkworms in 1959. Sam Woo/University of California Davis hide caption

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Sam Woo/University of California Davis

The first chemical identification of a pheromone involved Bombyx Mori silkworms in 1959.

Sam Woo/University of California Davis

Type the words "human" and "pheromone" into Google, and you'll get hundreds of thousands of hits.

"Most of them are trying to sell you something," says Tristram Wyatt, a pheromone researcher at the University of Oxford in England. But even though the word pheromone has been around for 50 years, Wyatt says no one has conclusively identified that kind of chemical signal in human scents.

Modern pheromone research began in 1959, when scientists reported they had discovered a chemical that acts as a sex signal in the silk moth Bombyx mori. Female moths produce a chemical called bombykol to attract males.

That same year, two researchers invented the word pheromone by combining two Greek words that mean "to excite" and "to transfer," says Wyatt, "so it was 'excitement transferred from one individual to another.'"

Over the decades, scientists have identified chemicals used to send messages between all kinds of animals, from fish to lobsters to elephants, according to a review published by Wyatt in the journal Nature.

But he says no one has found that kind of signaling molecule in humans, even though the idea of a sex attractant has captured people's imaginations. "The idea that there is something you can splash on yourself to make you irresistible is the ever-enduring hope," he says.

Back in the 1980s and 1990s, he says, various compounds were proposed as being human pheromones, including a family of steroids related to testosterone. "But there is no good evidence that these actually are the human pheromones," Wyatt says. "The evidence is always circumstantial and rather poor."

Wyatt says if you bought a jar of something called human pheromones, it would be "wasted money."

Human Pheromone Sciences, a company based in San Jose, Calif., sells what it calls "100 percent pure human pheromones" under the name "Natural Attraction." The Natural Attraction Web site states that "human pheromones are gender specific, naturally occurring substances that trigger specific 'mating' responses."

Bill Horgan, the company's chief executive, says a key active ingredient is androstadienone, a chemical related to testosterone. "Androstadienone is found in the human body, and people who are exposed to it, men and women, indicated a feeling of warmth and lack of negativity, improved positivity," says Horgan.

He says his company's products do not act on other people. "They're not sexual attractants," he says. "That's a key thing that we try to get across."

When told that some scientists say no chemical has been proved to be a human pheromone, Horgan insisted that studies show the chemical in his product has pheromone-like effects on mood and behavior. "We've seen it and others have seen it, independent of us," Horgan says. "In fact, some of them were detractors of us at first."

As an example, he cited a brief report showing that androstadienone increases nonverbal "courtship-like behavior" in women. One of the authors is Charles J. Wysocki, a well-known researcher at the Monell Chemical Senses Center in Philadelphia.

Wysocki, however, says the study was done years ago and that he had doubts at the time about its design. He says the analysis of the results and his collaborators' far-reaching conclusions made him uncomfortable, to the point where he asked to have his name taken off the paper.

When Horgan was informed of this by e-mail, he expressed amazement and responded that the science behind Human Pheromone Sciences' products is supported by other researchers who have studied the chemical.

Wysocki says that if someone is trying to sell you a bottle of human pheromones, "I'd be very skeptical. Caveat emptor."

Still, he says he does "not disavow the idea that humans communicate information about themselves via nonverbal, chemical means." In fact, his center has pursued the idea that human pheromones exist and that people's body smells can influence others in various ways.

For example, Wysocki did one well-controlled study showing that smelling men's underarm secretions can change the levels of a reproductive hormone in women's blood. "We did see an alteration in the hormone system that regulates the menstrual cycle," he says.

But male body odor is a complex mix of chemicals, and Wysocki can't yet say what in the mix might have caused the effect. So even though scientists have suggestive evidence that humans can communicate information via chemicals, he says, "what we are lacking is the actual chemical identities. That's where chemistry has to catch up with the behavior and the endocrinology."

Even if researchers conclusively identified a chemical that acts as a human pheromone, Wysocki says, it probably wouldn't have any kind of effect as dramatic as the first irresistible sex lure that scientists found in silk moths five decades ago.