Do Humans Have Pheromones?

Paul A. asks: Is there really such a thing as human pheromones?

Insects, such as the male silk worm using the pheromone Bombykol have long been known to attract mates through pheromones.

Moving over to the one humped camel, also known as the Arabian camel and dromedary, of all their adaptations, the grossest is probably the male dromedary’s proclivity to blow up a portion of his soft palate with air to the point that it protrudes up to a foot out of his mouth – as a sign to the ladies that he is hot to trot. With large, repugnant sacks hanging out of their mouths, male dromedaries begin the courtship. Using their spit to make a low gurgling sound that results in foaming at the mouth, they also mark their territory by rubbing their necks (where they have poll glands that produce a foul, brown goo) anywhere they can, and even pee on their own tails to attract a lady with their urine’s “female-attracting pheromones”.

Speaking of golden shower seeming pheromonel attraction, moving on from there, female giraffes also like to do the same to get male giraffes to stop going to town on each other and go to town on them instead. (Fun fact, 75% to 94% of male giraffe lovin’ is with other male giraffes instead of females.) If the female is particularly interested in a certain male, almost always the male with the longest neck around, she may even pursue him, rubbing her neck against him to try to get him to rub her rump so she can pee in his mouth.  In these cases, she will rarely play hard to get and usually will let him mount fairly quickly if her urine is to his liking. Once the female stands still long enough to allow the male, again usually the one with the longest neck around, to mount, coitus is extremely brief, lasting only a few seconds at most, once again proving it’s not the size of the neck, but how you use it.

This all brings us to alleged human pheromones. Unfortunately for the makers of love-potions, there has been no scientific proof that humans have the same capability, though this point is hotly debated, particularly as it’s relatively prevalent in many other creatures, sometimes not just for mating purposes, but to illicit other behaviors. On this note, that doesn’t mean we don’t have such pheromones, just that there has never been any 100% conclusive proof that we do. In fact, many researchers believe there are human pheromones positively affecting the mood of a prospective mate, but the exact molecule or molecules responsible haven’t been located. To better understand the topic, let’s explore pheromones and how our bodies respond, as well as what pubic, armpit, and facial hair potentially have to do with any of this.

To begin with, how do you define a pheromone? That definition is still the topic of hot debate. The most widely accepted definition, originally penned by the coiners of the term, Peter Karlson and Martin Luscher, in 1959 in their article Pheromones: A New Term for a Class of Biologically Active Substances, is “substances which are secreted to the outside by an individual and received by a second individual of the same species, in which they cause a specific reaction.”

If your definition is that broad, then it would appear humans do release pheromones; there have been countless studies showing certain odors, along with music and some types of lighting, can alter mood and physiological stimulation. And, in fact, as we’ll get to shortly when discussing pubic, armpit, and facial hair, there’s some evidence that these odors also help us determine subconsciously who we might be best suited to mate with to produce the healthiest offspring.

But first, as for the question- Can the way a person smells affect other people’s mood? The answer is absolutely, yes. But as for the more pertinent question- Is there a molecule that humans release that can specifically influence human endocrinology to illicit lustful desire? That answer is much more elusive.

Humans produce several different compounds in our urine, stool, breath, genitals, saliva, and glands within the skin. Proponents of the idea that humans do indeed have pheromones generally suspect skin glands are the source of said compounds. In fact, there are three types of skin glands- apocrine, eccrine, and sebaceous glands, and all of these can produce compounds that can become odorous and sensed by your nose, sinuses, in your oral cavity and then lungs.

As for the first on this list, apocrine glands are found in your armpits, nipples, ear canals, nostrils and some parts of your genitalia. They intermittently produce sweat containing cholesterol, triglycerides, fatty acids and other lipids. Those molecules are generally odorless until bacteria on your skin begin to break them down. Puberty is when apocrine glands typically become active, and they release secretions during times you’re experiencing anxiety, fear, pain or sexual arousal.

Eccrine sweat glands primary function is to control your body’s temperature through sweat. That sweat mostly contains electrolytes like sodium and calcium. It can contain lesser amounts of magnesium, phosphate, sulphate, and some proteins involved with your immune system (immunoglobulins and interleukins). The sweat is also generally odorless, except in certain cases like when you eat garlic.

On this one as a brief aside, this has to do with the fact that some of these sulfuric compounds in garlic get metabolized, eventually making their way into your blood stream. The primary smelly culprit here has been found to be allyl methyl sulfide, which is passed into the blood during the digestive process. Once it’s in your blood, it eventually gets passed out of your body through various bodily excretions, which includes being exuded through your pores and also passed into the air that fills your lungs. So as you breathe, the air goes into your lungs and is contaminated by the allyl methyl sulfide; this in turn causes your breath to continue to smell even if you’ve cleaned your mouth out. On top of that, this will also be exuded from your pores.  This ends up causing your whole body to smell, not just your breath.  As you are excreting this sulfide, you essentially are wearing a stinky perfume. This effect lasts as long as it takes for your body to get rid of the smelly sulfuric compounds, which can be anywhere from a few hours to as much as a day after eating the garlic.

Going back to pheromones, sebaceous glands are found almost everywhere on the body, except the palms of your hands and the soles of your feet. They produce Sebum containing triglycerides, waxes, squalene, and fatty acids. The primary purpose of Sebum is to lubricate hair and skin. It can also have antibacterial properties, and is said to have a pleasant odor until various bacteria get involved. Like Apocrine glands, Sebaceous glands become active during puberty and, when they become clogged, produce the zits teenagers everywhere flaunt with disdain.

The question then becomes do any of these three glands, or their subsequent molecules, affect the opposite sex in an attractive way?

The molecules most researchers seem to look at when studying pheromones are steroids, such as Androstadienone, Estratetaenal, Androstanol, and Androstenone. All three sweat glands can, in some way, affect or be effected by, steroids.

Why do researchers focus on these in their search for human pheromones?  Steroids fit the concept of an externally secreted hormone; they’re one of the compounds linked to reproductive behavior; they’re commonly present in the sweat from your armpits, while also found in saliva, urine and semen; men tend to have higher concentrations than women, and women are more sensitive to them than men; many humans have been shown to be able to distinguish the difference between male and female sweat, with the differences in steroid concentration being proposed as one potential reasons; and, finally, one steroid (androstanol) seems to have no known function in humans.

As for how humans detect pheromones, if they do exist, the organ involved here is the vomeronasal, or Jacobson’s, organ (VNO). This little libido-detector is what gives animals the ability to communicate via pheromones. Many perfume manufacturers, and those who wholeheartedly believe in human pheromone communication, point out that humans have this organ at the base of their nasal septum. They also tend to say, when stimulated, it will communicate with the hypothalamus. This portion of the brain is responsible for many of the autonomic processes involved with your nervous system, including potentially affecting mood.

Unfortunately for proponents of this idea, the VNO appears to be nonoperational in humans. After a specific step in fetal development, providing for the secretion of sex hormones by the anterior hypophysis, the VNO’s neural connections go away. In fact, the genes responsible for making the ion channels that allow for communication between the brain and the VNO are nonfunctional in humans. The adult brain has no way to detect the information even if there was a connection in the form of an accessory olfactory bulb.

Nevertheless, countless studies have attempted to prove pheromone communication does occur in humans. Going back to armpit and pubic hair and the potential connection there, as with many things in nature, the leading theory as to why we still have pubic and underarm hair is to increase the chances of getting lucky. This is perhaps backed up by the fact that unlike hair on the top of your head, armpit, thick pubic hair, and potentially facial hair tend to show up during puberty, around the same time your apocrine sweat glands become active and begin secreting an oily substance containing a variety of proteins and the like. These apocrine glands are, among a few other places, concentrated in your armpits and genitals, unlike your other main type of sweat gland, eccrine glands, which are distributed pretty well throughout your body. Pubic and armpit hair also usually begins to thin out significantly starting around when people hit their fifties, perhaps another indicator it’s all about finding a compatible mate.

More specifically, it is theorized by some that the hair exists for the purpose of getting soaked in potent mate-attracting pheromones. This initially odorless secretion turns into a musky smell after various microbes have their way with it; a potential mate picks up the scent and their body uses it as an indicator that you are ready to make the beast with two backs.

Further, whether consciously detected or not, each individual gives off a slightly different scent thanks to something known as the Major Histocompatibility Complex (MHC).  Studies, such as one having women smell the armpits of t-shirts previously worn by various men who in turn wore no deodorant or the like, have shown that people with dissimilar MHC feel more attracted to each other (and, in fact often become aroused when catching a whiff of such a person). While the research is not yet wholly conclusive, there is even some evidence that when these two with such differing MHC make a baby, they can expect a lower than average rate of miscarriage. It is also thought that greater genetic diversity results in offspring being less susceptible to disease, both suggesting an evolutionary benefit to heading what your nose is telling your brain about a person based on apocrine secretions.

Thus, the theory goes that because the hair naturally wicks these secretions away from the skin, it allows for better ventilation and a more prominent smell than you’d achieve without it.

Further adding fuel to the fire is beard and pubic hair growth rates and when they peak. While if it was for warming purposes, you’d think winter would see the highest growth rates in these areas, in fact, it’s the opposite- studies show summer is king here, and winter sees the lowest.

This actually makes sense when you look at the underlying mechanisms behind beard hair growth and its hypothesized connection to mating.

Specifically, in the study, Seasonal Changes in Human Hair Growth, published in 1991, looking at a group of British men aged 18-39, it tracks their beard growth and activities for 18 months. Incidentally, the researchers also confirmed what others have likewise shown- that scalp hair, used more for warming purposes, for example, has a peak amount of hair in the anogen (growth phase) in the winter, around February/March at approximately 90%, then falling steadily from there until September then climbing back up. They also directly measuring about 60 hairs lost per day from the scalp at peak telogen phase time (in the summer) and about half that rate during the winter.

As for beards, this is almost the exact opposite. They observed that the growth rate of beard hair actually peaked in June and July and was at its lowest in January and February. Not a subtle difference, the peak growth rate in the summer months was 38% faster than in the lowest growth rate months of January and February.

Given other studies have shown sperm count, semen volume, and sperm mobility also peaks in the summer for many men, and pubic hair also more or less seems to track with beard hair cycle timelines, once again, it’s hypothesized that pubic hair has remained on humans (along with armpit hair) to help attract the opposite sex via certain pheromones.

Further, beards have likewise been connected to mating via a surprising number of studies looking into the connection with beards and attractiveness. On this, studies pretty consistently show that, while there are of course exceptions, women en masse find men with stubble to short beards the most attractive. However, there is another element that may favor men with long, full beards in terms of actual desire to mate with said man. For example, in the 2013 study The role of facial hair in women’s perceptions of men’s attractiveness, health, masculinity and parenting abilities the researchers found that while the majority of women perceive men with long, thick beards as more masculine then men with closely trimmed beards or clean shaven, when women are most fertile in their cycle, their ratings of the masculinity of men with full beards increased even more.  Further, the women in the study also consistently rated men with long, full beards as more likely to be better fathers and more socially mature. As the researchers sum up of their research, this “suggest[s] that an intermediate level of beardedness is most attractive while full-bearded men may be perceived as better fathers who could protect and invest in offspring.”

Further, this and other studies have likewise shown that women consistently rate bearded men of all levels as healthier than their bald-faced compatriots. Thus, all combining to potentially give a benefit to faster beard growth at times when male sperm counts and motility are the highest- the warmer months when historically resources for baby making are at their peak.

On a related note, many studies show that the body’s chemistry changes from within as we get older producing a certain scent.  Some may describe it as musty.  Some may call it stale.  Maybe a bit medicinal. Whatever the case, a recent research study done by Johan Lundström of the Monell Chemical Senses Center published in PLOS ONE tested the odors from the underarms of middle-aged adults and the elderly. The result?  Middle-aged men smelled the worst, according to those surveyed.  The good news?  Grandpa was considered second-best, and actually pleasant smelling. Middle-aged women came out on top of the list of most-enjoyable body odors.

The study was conducted by attaching absorbent pads to the lining of the armpits of shirts. The shirts were then worn by volunteers of various ages for five consecutive nights while they slept.  In order for other smells not to seep when the shirts weren’t being worn, they were stored in sealed plastic bags during the day.  The volunteers were also required to use scentless soaps and shampoos during the experiment and not to eat or expose themselves to strong smelling external things like perfume or cigarette smoke.

After the five days were up, the pads were collected and placed in sealed jars ready to be opened and sniffed by other volunteers to judge the smelliness and to see if people could correctly identify the general age of the person who wore the pad (young, middle-age, and old-age).

The results? The volunteers were able to correctly identify which pads were worn by old people most of the time, though that was about the extent of the accuracy.  While they did also detect a distinct difference between the middle-aged and young, they were not able to accurately identify which was which in most cases.

So what exactly is thought to be causing this change in smell as we age?  It’s still somewhat up for debate, but it is thought that there are many factors involved.  One factor, according to physician, Eric Shapira, is simple dehydration. Older people tend to be less thirsty, which results in them being predominately more dehydrated and shedding more dry skin.  Dead skin cells can carry a musty smell.  In addition, Shapira notes that older people see a decline in oral hygiene over the years due to less efficient brushing.  Oral hygiene, of course, can also affect one’s scent.

A more scientific approach to this question was taken by a team of Japanese researchers in 2000.  They discovered that a concentration of the chemical 2-nonenal, which is an odoriferous substance found in sweat and on your skin, increased as people aged, with people in their 70s having as much as three times as much of it as middle-aged individuals. It’s thought that the extra 2-nonenal is coming from the breakdown of more prevalent omega-7 fatty acids on our skin as we age.  (Interestingly, besides being perhaps a major culprit in the smell of an elderly individual, 2-nonenal is also a key component in the smell of beer.)

An elderly person’s living environment is also thought to be a factor.  How many of us know a relative who keeps, or hoards, everything from years gone by? Brenda Thompson of Tri-Country Home Nursing says, “All those old books and papers, old linens and clothes — they all harbor dust and dampness and give off a musty odor that can pervade the whole house. If you moved into that house in 1945, those books may have been there for 60 years. I’ve seen drapes that have been there that long, too.”

Here’s another odd thing about the changing of how we smell as we age: as we grow older, nearing age 80, males tend to smell more and more like women, with this change thought by some to be hormonal based, though exactly what’s going on isn’t yet perfectly clear.

Going back to potential pheromones, once again, despite a slew of studies on our ability to sniff things out about each other from potential genetic compatibility to if we are old or young, as well as the potential role certain post-pubescent hairs on our body might aid in this and mating, finding definitive proof that any of this has to do with our sexual attraction to one another, has been elusive to date. But adding more wood to the potential fire is that there are also studies that show people with higher levels of specific hormones are more attractive than others, BUT, once again, none have definitively shown specific cause and effect.

What does science say will make someone more attractive? Studies suggest long distance runners have an advantage. Possibly due to having higher testosterone levels than the average person. Facial symmetry has also been shown to be important. Most likely because it signals prospective mates that the individual has good genes. Finger length, specifically your ring finger, because it has been shown to relate to testosterone levels within the womb. Thus, those with longer ring fingers tend to have higher sperm counts, increased fertility, and better cardiovascular health, and interestingly, more symmetrical faces. (Also interestingly, ratio of finger size in men, rather than overall length, is strongly correlated with penis size, as we’ll get to in the bonus facts in a bit.) Lastly, body shape and the specific way you smell have been shown to be contributing factors in attractiveness.

In the end, humans can release molecules that affect the mood of the opposite sex. Fortunately for candle makers, and Barry White album sales, no known molecule has been definitively found to induce sexually ravenous behavior. But don’t worry, since showering before a date is always a good idea, and many of us shave our naughty bits at least to some extent, you’ll probably wash off any sex-molecule anyway, and will have to simply rely on your charm and physical appeal, or for some of the men among us, the size of your… bank account. With successful men in this way, generally shown to be more attractive to an extent to many women, though hilariously studies show factors like height, or rather in this case in the diminutive sense, can strongly over power the ability to be a phenomenal provider in how attractive women rate men. So… sorry short guys… Maybe just get in phenomenal shape, grow a beard, rock that personality, and develop a great sense of humor.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

Bonus Fact:

Speaking of size of things potentially mattering, contrary to popular belief, studies have consistently shown that the size of a guy’s feet or the overall size of their hands is not related to their member’s erect measurement. However, a man’s fingers do give a strong clue as to their probable penis size- but the overall length of the fingers is not what’s important here.

For instance, a study published in the Asian Journal of Andrology in 2011 found that the ratio between the 2nd and 4th digits on the hands strongly correlates with the overall length of an individual’s penis. Specifically, Dr. Ho Choi and et al. state;

Univariate and multivariate analysis using linear regression models showed that…. only digit ratio was a significant predictive factor for stretched penile length…

In a nutshell, the lower the ratio- how much shorter the index finger is than the ring finger- the longer the penis will probably be when erect. (And if you’re wondering, flaccid penis length is not an accurate predictor of erect penis length.)  More specifically, you can calculate your ratio by taking the length of your index finger (measured from the crease where it meets your hand, to the tip) and divide it by the length of your ring finger. The shorter your index finger is compared to the ring finger, the lower the ratio will be and, if you’re a man, the longer your penis probably is.

So why does the ratio of the index and ring finger lengths correlate to erect penis length? In the beginning, female and male genitals are pretty much the same. This is because they develop from the same cluster of tissues (gonads).  In males, somewhere around weeks 7-9 of gestation, the gonads begin secreting two hormones- Anti-müllerian hormone (AMH) and testosterone. AMH prevents the development of the ducts that eventually turn into the fallopian tubes, the uterus, and upper vagina.

Once the gonads begin secreting testosterone, some if it (around 5-10%) gets transformed into another hormone called dihydrotestosterone. Both testosterone and dihydrotestosterone will attach to androgen receptors, which affect the growth and development of many different body systems.

Notable here, dihydrotestosterone attaches to androgen receptors on tissues that eventually develop and combine into the penis and scrotum. Low levels of this within the womb, or later during puberty, may result in an underdeveloped or malformed penis.

So to sum up here, penile growth in the womb is stimulated and affected by testosterone, dihydrotestosterone, and androgen receptors. Circulating amounts of the two hormones, combined with the associated androgen receptor stimulation, will determine penis size.

So what about fingers? Circulating testosterone in the womb will affect other body parts as well- pertinent to the topic at hand, including the ratio between the 2nd and 4th digits (index and ring fingers).

Why does testosterone affect digits differently? For that, I’ll have to get a little more technical, but essentially the activity mediated by androgen receptors, and estrogen receptor-a, is higher in your ring finger compared to your index finger. This is regulated by the structure of genes controlling the process for the bone growth of your fingers, called endochondral ossification. The spread of chondrocytes will determine the length of your finger, and this expansion is higher in the ring finger compared to the index finger.

When you decrease the activation of androgen receptors during the narrow window of digit development (usually completed by week 13 of gestation), you will decrease the length of your ring finger. This activation is attributed to amount of testosterone and DHT circulating throughout the tiny fetus. Conversely, if you decrease the activity of the receptor estrogen-a (the ones being stimulated more when you’re female), you will get a longer ring finger.

Based on this physiology, it has been long known that you can predict prenatal hormone exposure based on the ratio of these two fingers. Since both penile length and the ratio of the ring and index finger is basically a result of the amount of testosterone and DHT circulating in utero, there is a correlation between that ratio and the length of a man’s favorite appendage.

As you might have guessed from all this, the ratio between the lengths of one’s index and ring fingers is usually quite different in men and women- men tend to have shorter index fingers than ring fingers; women tend to have their index fingers either the same length or longer than their ring fingers.

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