We humans are more complex. Certainly, how we smell to each other affects our hormones, which may influence behavior, sexual and otherwise. For example, the odor of perspiration plays a role in the synchronization of the menstrual cycles of women who live or work together. In men, the scent of a T shirt worn by an ovulating woman leads to testosterone levels going up, while the scent of a woman's tears of sadness causes testosterone levels to drop. Human odors are linked with behaviors as diverse as the fear response and mother/baby bonding.
Women are known to unconsciously sniff out biologically relevant information from underarm sweat.
Evidence of Human Pheromones
The strongest evidence for pheromone signaling between humans had been revealed by Dr. Martha McKlintock, who discovered in 1998 that the menstrual cycles of women living together tend to synchronize because of the chemical messages released in their sweat.
The latest study, which appears in this week's issue of the journal Neuron , used PET (positron emission tomography) scanning techniques to analyze the brains of 24 men and women while they smelled chemicals almost identical to the naturally produced sex hormones estrogen and testosterone.
Dr. David Berliner, an expert in the field of chemical signaling and CEO of Pherin Pharmaceuticals, which produces synthetic pheromones, says: "These findings corroborate that human pheromones do exist, and that women can communicate chemically with men and vice versa. This is a very important finding because it shows specific areas of the brain that are activated by these chemicals."
The scientists, led by Dr. Ivanka Savic of the Karolinska Institute, found that the hormone-like smells "turn on" the brain's hypothalamus, which is normally not activated by regular odors.
They also found the brains of men and women respond very differently to the hormones.
Women's hypothalami are activated when they smell the chemical similar to testosterone but not to the estrogen-like substance, whereas men's hypothalami have the opposite response: They are turned on only by the estrogen-like chemical and not the testosterone-like one. There is also sexual disparity between the specific sub-regions of hypothalamus that are activated.
In other words, the way we chemically perceive the opposite sex is very different than the way we perceive members of the same sex. Researchers believe this could explain why some of our behaviors are gender-specific.
In the German study, researchers from Ruhr University in Bochum found that the specific human scents activated the vomeronasal receptor (VN1R) that humans have in their noses. This is the organ that acts as a pheromone receptor in other mammals but hasn't been shown to be active in humans--until now. Just as importantly, using functional magnetic resonance imaging (fMRI), the researchers also found that smelling these scents activated areas in the brain's limbic system, which is associated with emotions, memory and motivation.
Can Pheromones Make Us More Sexually Attractive?
If these pheromones turn on areas of the brain that control mood, hormones and sexual behavior, one might then ask: "Can these chemicals make us more attractive?"
The answer is: Maybe. Researchers at the University of Chicago and University of Utah have found that the same sex hormone-like chemicals used in the Swedish study can in fact have a pheromone effect by producing changes in mood, heart rate, breathing, and body temperature. However, there is currently no indication these chemicals can actually increase sexual arousal or attraction.
Many perfume companies have tried to capitalize on the potential sex-specific effects of these chemicals by adding them to their fragrances. But most of these companies add hormones from animals such as pigs and deer, so they probably don't work. Pheromones are generally species-specific, so a perfume enhanced with pig pheromones is really only useful for other pigs.
The promotions of one company that adds human hormones to its fragrances claim the additives will "put you and your partner at ease, boost your confidence, and contribute to a feeling of well being." The general idea is that pheromone perfume can replace our naturally produced pheromones that have been washed off through bathing and hidden by layers of clothing.
If these claims are true, pheromones may make us more attractive to potential mates by bringing out our best qualities and allowing us to appear more self-assured and relaxed. That "feeling of well being" may also make us a lot more pleasant to be around.
Pheromones as Therapeutics
The ability of these sex hormone-like chemicals to activate areas of the brain that control hormones indicates they may have more broad-ranging therapeutic value as well.
For example, there is significant research now on creating bioidentical pheromones with hopes that it will be effective in decreasing symptoms of anxiety disorders, premenstrual syndrome in women, and prostate enlargement in men.
Berliner has personally tested many of these compounds. "I love it!" he enthuses. "And it takes only seconds to work. It is very hard to explain with words, but it makes you feel relaxed. All of a sudden your internal life changes for the better, although the outside world has not changed at all."
"Many perfume companies have tried to capitalize on the potential sex-specific effects of these chemicals by adding them to their fragrances. But most of these companies add hormones from animals such as pigs and deer, so they probably don't work. Pheromones are generally species-specific, so a perfume enhanced with pig pheromones is really only useful for other pigs."