Love Is All in Your Head -- Or Is It in Your Genes?

Feb. 14, 2001 -- Legend has it that when Napoleon Bonaparte wrote Josephine to arrange a love tryst, he said, "I'm coming home -- please don't wash." Recent research on the scientific basis of love suggests that the famous general may have been onto something that guaranteed his success in the bedroom as well as on the battlefield.

Armpit sweat broken down by bacteria may not sound very appealing, but that's the origin of pheromones, those elusive, odorless chemicals given off in response to sexual stimulation or even romantic fantasy. In animals including mice, dogs, and insects, these chemicals attract the opposite sex and initiate mating behavior.

"In humans, the effect is quite different, because they have to inhale their own pheromone for it to work," Peter Pugliese, MD, PhD, tells WebMD. From the nose, the pheromone travels to a part of the brain involved in emotions and sex drive.

"This makes the person aware of their own attractiveness and allows them to project a heightened sense of approachability," says Pugliese, a private skin physiology consultant to Philosophy Cosmetics. "In married couples, pheromones might cause a renewed interest in the other person, leading to feeling closer and being more attentive -- not necessarily to sex."

But don't write off the power of pheromones as an aphrodisiac just yet. A 1998 study from the Athena Institute for Women's Wellness Research in Chester Springs, Pa., documented the sexual activity of 38 young to middle-aged heterosexual men while using pheromones. Users of pheromones, but not of an inactive control substance, had increased frequency of informal dates, affectionate gestures, sleeping next to a romantic partner, foreplay, and sexual intercourse.

As frequency of masturbation did not change, the researchers concluded that pheromones increased the sexual attractiveness of men to women, and therefore sexual behaviors requiring the woman's interest and cooperation, rather than sex drive itself.

Hoping to capitalize on the purported effects of pheromones, Philosophy Cosmetics markets an odorless elixir of pheromone concentrate called "Falling in Love," for women only, to increase their sense of well-being.

Evidence, albeit unsubstantiated, from Victoria's Secret suggests "spectacular results" in women using the product, even those who considered themselves to be unattractive, Pugliese says.

Before you rush out to buy stock in this company, though, be advised that scientists are still arguing over whether humans even have a specialized sensory organ that detects pheromones, known in rodents as the "vomeronasal organ." In last month's issue of Annual Reviews of Psychology, Richard L. Doty, PhD, a professor of otorhinolaryngology at the Smell and Taste Center of the University of Pennsylvania in Philadelphia, reviewed the evidence and called it "controversial."

"Humans might have similar [structures] in the nerve cells lining the nose, but we don't yet know how they're activated," says Frank Zufall, PhD, an associate professor of anatomy and neurobiology at the University of Maryland in Baltimore.

When we speak of the chemistry of love, it's not just an idle expression. Different chemicals in the brain, or neurotransmitters, play different roles at each stage of the mating game.

"There are three different types of love -- lust, romantic love, and long-term attachment -- each associated with different neurotransmitters, all hardwired into the brain," Helen E. Fisher, PhD, tells WebMD.

"Lust, that emotion that chases us out of the house and drives us to find a partner, is related to bursts of testosterone," says Fisher, a professor of anthropology at Rutgers University in Newark, N.J.

Romantic love, she says, is related to abnormalities in the neurotransmitters serotonin, dopamine, and norepinephrine, making it biochemically similar to obsessive-compulsive disorder, a psychiatric illness where thoughts of a single subject dominate the patient's life.

Fisher has interviewed romantic lovers who tell her that they spend 85% of their waking moments fantasizing about their loved one. "In romantic love, we can't stop thinking about the person we're in love with," she says.

When you're in love, it's in your blood as well as in your head, according to research from the University of Pisa in Italy. Subjects falling in love resembled patients with obsessive-compulsive disorder in terms of neurochemical changes involving platelets, those blood cells involved in making blood clot and wounds heal.

"I did not discover why we fall in love, but only that romantic lovers resemble patients with obsessive-compulsive disorder in this platelet abnormality, which may underlie the similar thought process," researcher Donatella Marazziti, MD, tells WebMD. "This is only a small tile in the complex mosaic of love, which is certainly also something more than mere biology."

In romantic love, we feel elated and giddy, and can't sleep or eat, because of increased levels of dopamine and norepinephrine. "This phase evolved so we could distinguish between potential partners," Fisher says.

When we're in love, dopamine, nicknamed the "pleasure chemical," gives us a "high," according to James H. Fallon, PhD, a professor of anatomy and neurobiology at the University of California at Irvine.

"Dopamine is the great motivator in the brain that is absolutely necessary to act ... to walk over to the person we've just seen and start a more serious approach," Fallon says.

Dopamine can be stimulated artificially by alcohol and drugs. Along with other brain chemicals, it also gives us those physical clues that we're falling in love -- heart racing, pupils dilating, and a light sweat -- turning on pheromone production.

Genetic differences in body chemistry may create different pheromones, so that prospective mates may be subconsciously "turned on" or "turned off" by subtle chemical messages. Commercially produced pheromones are therefore unlikely to have universal appeal, according to Fallon.

Another spirit in the heady cocktail making us intoxicated with romantic love is phenylethylamine (PEA), according to Hector Sabelli, MD, PhD, a researcher at the Chicago Center for Creative Development in Illinois. "I believe that PEA may be the hormone of libido, but there's only circumstantial evidence at this point," Sabelli tells WebMD.

Sabelli's research showed that high PEA levels help explain increased sex drive and activity in the manic phase of manic-depressive illness, while low PEA levels reflect loss of libido in depression. PEA is effective when given by mouth, but like Viagra, could be dangerous in patients with heart disease.

The final phase of love, the one that leads to diamond wedding anniversaries, is a calm, secure feeling of attachment to a long-term partner. "This is important to conserve our mating energy, bonding with only one partner at a time," Fisher says.

Oxytocin is the hormone thought to be responsible for this phase of love, as well as for mother-child bonding. Fallon calls it the "cuddling hormone," as it is released by touch "done with the right rhythm and pressure."

Could there be a genetic basis for long-term commitment? Perhaps at least in the prairie vole, an extraordinarily faithful rodent, explains Thomas Insel, MD, director of the Center for Behavioral Neuroscience at Emory University in Atlanta.

From their first mating, prairie voles bond for life. The male defends the female from all other males and mates with her to the exclusion of all other females. Even when their mate is removed from the colony, 80% of males refuse to mate with any other female.

Insel discovered that oxytocin and vasopressin, a nerve chemical linked to memory, are released in the rodent's brain at first mating. If Insel artificially changed the levels of these hormones, he could wipe out the lifetime bond.

Even more extraordinary, Insel found the gene responsible for this behavior and developed a mouse carrying this gene. He was hoping to create a "monogamouse" that would remain faithful to one mate, unlike most mice who mate with any available female. But, alas, the experiment was unsuccessful. "'Monogamouse' does not exist," Insel tells WebMD.

While Insel does not think his research might lead to any type of love potion, he hopes that it might eventually provide an approach to autism, a disorder in which children don't connect emotionally with people around them.

Fallon believes that science might eventually assist Cupid with just the right mix of nerve chemicals to intensify attraction, romantic excitement, and long-term bonding. But probably not any time soon.

"If we really understood the [science], we could increase or decrease the threshold for falling in love," Semir Zeki, PhD, tells WebMD. "A neurochemical to manipulate this emotion would be very heavily controlled, and not advisable to use," says Zeki, a professor of cognitive neurology at the University College of London in England.

By using functional MRI scans, Zeki studied brain activity associated with romantic love. Scans done while subjects were viewing pictures of their love interest were compared with scans done while they viewed pictures of platonic friends, and the scans were different.

"The sentiment of love triggered by a face is controlled by a unique pattern of small areas in the brain heavily interconnected with each other," Zeki says.

Fisher is now analyzing her own neuroimaging data from subjects in romantic love and predicts that she will find altered activity in brain systems using dopamine and norepinephrine.

"We have an enormous amount to learn about the human sexual response," Pugliese says. "Cows in heat bellow so that males can find them, but they still exchange pheromones by sniffing each other's genitals before mating. With humans, it's far more subtle."

Until science concocts the best recipe for romance, you might do well to stick to the old standbys for Valentine's Day. According to Fallon, chocolates can give your lover a buzz by stimulating PEA production, while soft lights, turning up the heat, and romantic music will get the oxytocin flowing. For shy lovers, a cocktail might loosen inhibitions, but too much is self-defeating. Science suggests that at least one way to a man's heart is through his eyes, so an alluring negligee can't hurt.

You might want to think twice about Napoleon's advice not to bathe, though, remembering that he also was quoted as saying, "Not tonight, Josephine."