By Dr. Mercola
Insects, fish, and non-human mammals all have pheromones, which are chemical signals that influence the behavior or physiology of other members of the same species. Pheromones may, for instance, divulge an animal's age, gender, and emotional state, along with their social and reproductive status.
Whether or not humans release pheromones, and what role they play considering humans have multiple other systems to acquire information, is a subject of debate and considerable research.
While the underpinnings of human pheromones are still being discovered, it's clear that humans do communicate on a chemical level and, according to The Monell Chemical Senses Center, "It's much more than we thought."1
Pheromones Likely Influence Sexual Attraction
If you've ever found yourself inexplicably attracted to a stranger you've just met, it could very well be their chemical signals that you find irresistible. Humans tend to be attracted to those with a dissimilar genetic make-up to themselves, which is signaled by subtle odors (though you probably don't consciously recognize).
This ensures genetic diversity for the species. For instance, it's thought that each of us has a unique "signature smell" due to a collection of proteins called the major histocompatibility complex (MHC). MHCs help to regulate your immune system, and there's evidence that they also play a role in your selection of a mate.
Ideally, you would select a partner with MHCs quite different from your own, as this would diversify your child's immune system, making them better equipped to fight off pathogens.
In one study, women sniffed shirts worn by men and selected those which they'd most like to socialize with. The women tended to choose men with dissimilar MHC… except when they were taking birth control pills.
When a woman is on the Pill, her odor preferences change. The Pill essentially mimics pregnancy, and when a woman is pregnant, she tends to prefer the scent of men with similar MHC as her own—perhaps as a biological cue to now seek out and bond with supportive family members as opposed to potential mates.
What this means is that when you're taking a hormonal contraceptive, you interfere with your biology and risk producing a hormonal imbalance that might make you more attracted to men with similar chemical makeup.
If you were on the pill when you met your mate, you might, therefore, feel less attracted to him when you stop taking it. The study's lead author noted:2
"Choosing a non-hormonal barrier method of contraception for a few months before getting married might be one way for a woman to check or reassure herself that she's still attracted to her partner."
Scientific Proof of 'Chemical Attraction'
There are many fascinating studies that show there really can be an unconscious chemistry between two people. Often, this appears related to estrus, or the time in a women's menstrual cycle when she's most fertile and able to conceive.
One study involved professional lap dancers in a gentlemen's club. The women earned the most tips just prior to ovulation, the most fertile period, and the least tips during menstruation.3 Women taking birth control pills, however, did not show a significant difference in tips throughout their cycle.
A separate study involved men smelling t-shirts worn by women who were about to ovulate. The men had higher testosterone levels than when they smelled t-shirts from women not about to ovulate or those with a control scent.
According to the study:4
"Hence, olfactory cues signaling women's levels of reproductive fertility were associated with specific endocrinological responses in men--responses that have been linked to sexual behavior and the initiation of romantic courtship."
There are actually a growing number of studies showing that scent communication may play a central role in mating… not just in non-human mammals but in humans as well. For instance, men may perceive women's "high-fertility body scents" (collected near ovulation) as more attractive than their low-fertility body scents.5
A Woman's Fertility Status May Influence a Man's Behavior
Research even shows that subtle signs of women's fertility influences men's mating cognition and behavior and facilitates "psychological and behavioral processes associated with the pursuit of a sexual partner." According to one series of studies:6
"In Study 1, men exposed to the scent of a woman near peak levels of fertility displayed increased accessibility to sexual concepts. Study 2 demonstrated that, among men who reported being sensitive to odors, scent cues of fertility triggered heightened perceptions of women's sexual arousal.
Study 3 revealed that, in a face-to-face interaction, high levels of female fertility were associated with a greater tendency for men to make risky decisions and to behaviorally mimic a female partner. Hence, subtle cues of fertility led to a cascade of mating-related processes-from lower order cognition to overt behavior-that reflected heightened mating motivation."
The opposite may also hold true, in that women who smelled men's sweat reported feeling less tense and more relaxed than women who smelled a placebo. Researchers also detected a shift in luteinizing hormone, which typically surge just prior to ovulation (but also peaks hundreds of times during the menstrual cycle).7
6 Weird Facts About Kissing
While we're on the topic of attraction, you may be surprised to learn that that first kiss (or the many after) may serve a very important purpose. Actually, it may serve multiple purposes. As reported in TIME:8
1. Kissing May Build Your Immunity
A 10-second kiss may transfer 80 million germs from one mouth to another. As you pass these bugs around, your body can build up immunity to them. One such "bug" is cytomegalovirus, which lurks in saliva. It normally causes no problems, but it can be extremely dangerous if caught while pregnant and can kill unborn babies or cause birth defects.
Research suggests that kissing the same person for about six months may provide optimum protection and allow women time to build up immunity against cytomegalovirus. Writing in the journal Medical Hypotheses, researcher Dr. Colin Hendrie from the University of Leeds said:9
"Female inoculation with a specific male's cytomegalovirus is most efficiently achieved through mouth-to-mouth contact and saliva exchange, particularly where the flow of saliva is from the male to the typically shorter female."
2. Kissing Is Another Way to Assess Your Potential Mate
Women rate kissing differently at different points in their menstrual cycle. When they're close to ovulation, romantic kissing is rated as more important.10
3. It May Boost Libido
French kissing is enjoyed by both men and women in long-term relationships, but in short-term relationships it's the men who tend to prefer it. According to Laura Berman, PhD, assistant clinical professor of ob-gyn and psychiatry at the Feinberg School of Medicine at Northwestern University: "One theory is that their saliva transfers testosterone to the woman, which in turn increases her sexual desire."
4. Boost Your Mood
Kissing triggers the release of feel-good chemicals like endorphins while lowering levels of the stress hormone cortisol.
5. Strengthen Your Relationship
People who report frequent kissing have greater levels of sexual satisfaction in their relationship. Men who kiss frequently also report feeling three times happier in their relationship than men who do not.
6. The Longest Kiss…
The longest kiss award goes to Ekkachai Tiranarat and Laksana Tiranarat, who kissed for 58 hours, 35 minutes, and 58 seconds in 2013!
Beyond Romance: Chemical Signals May Influence Mood, Social Support and More
Chemical signals aren't only reserved for attracting a mate. They influence a complex array of biological processes and human relationships. For instance:
- Women who sniffed fear-induced sweat became more mentally alert and intelligent, according to a study in Chemical Senses.11 According to researchers, "Humans distinguish between fear and other emotional chemosignals based on olfactory cues."
- Women who sniffed the scent of 2-day-old babies had increased activity in the reward-related areas of their brain.12
- Exposure to other women's pheromones may cause women's menstrual cycles to speed up or slow down.13
- Odors collected from pads in the underarm and breast area of breastfeeding women changed menstrual cycle length and sexual motivation in other women.14
- Chemical communication may convey social support, for instance among a support group for breastfeeding women.15
So while it seems clear that chemical signals, including pheromones, play a role in sexual attraction and finding a mate, they likely influence other key relationships as well, such as those between you and your child and, possibly, even close friends. These signals may help you avoid potentially threatening situations and may one day even be harnessed to help diagnose diseases (some of which also emit a unique odor production). So you might want to think twice about covering up your own natural scent with artificial perfumes. As neuroscientist Charles Wysocki observed:16
"With every little piece of information we gain, we scrape away a little bit of blackness on the window. As we peek through a little more and begin to see that humans have the potential to communicate with chemical signals, we're finding that human behavior and physiology respond much more to chemical communication than we originally believed."