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Human pheromones: Welcome to the party

Do humans have Pheromones?
We know that pheromones exist for insects, but what about humans? This is a complicated and controversial area. Odours and fragrances can certainly alter our moods, emotions and feelings, but is there evidence that unique chemicals exist, namely pheromones, which specifically alter such states? Chemical isolation of mammalian pheromones has been reported in almost every animal, including elephants, rabbits, pigs, mice, goldfish and deer. For example, interestingly, elephants and some moths share the sex pheromone (Z)-7-dodecen-1-yl ethanoate. Male elephants are unlikely to be attracted to a female moth because she releases such small quantities, only picograms per hour - so a male elephant would not notice it, but a male moth does.
In male mice urine, the (S)-enantiomer of SBT is responsible for its green, nutty smell and it is a potent attractant. Only the (S)-enantiomer is excreted in urine - the (R)-enantiomer produces a different response in mice. Although the existence of pheromones in mammals is widely accepted, some argue that in mammals, unlike in insects, these chemicals do not ‘release’ behaviours in a simple manner. While most insect pheromones produce a stereotyped response even under totally inappropriate circumstances, it is difficult to apply this simple ‘releaser’ idea to much of mammalian social behaviour, whether elicited in part by odours or not. Humans excrete or secrete many different chemicals via, for example, their urine, breath, saliva, and skin glands.
Many proponents of the human pheromone concept assume that skin glands are the source of the active pheromonal agents. But, the ability of humans to determine the sex of another human on the basis of odours, appears to depend on the intensity or pleasantness of the involved odours, not on the chemical makeup of the secretions.
Steroids, like androstenone, are often described as human pheromones, perhaps, because of their musk-like ‘animal-like’ odour, their presence in bodily secretions including sweat and urine, and their role in mammalian reproductive behaviour - androstenone is found in the saliva of male pigs and it can send a female, when in heat, to assume a mating stance. It is the active ingredient in ‘Boarmate’ used by pig farmers to test sows for timing artificial insemination. However, steroids do not contribute much to the generation of prototypical human body odour, which arises largely from a mixture of C6-C11 normal, branched, and unsaturated acids, including the two shown acids here. Indeed, in stark comparison to these acids, a significant number of people cannot smell androstenone and related steroids.
You may remember the highly published research showing that the menstrual cycles of close friends or dormitory roommates synchronize over time. This has been linked to pheromones, although no chemical identification of the alleged pheromone has yet been made. Indeed, subsequent studies have also doubted whether this synchrony actually exists. So, despite over half a century of study, we have yet to find direct evidence of the existence of pheromones in humans. However, the failure to identify human pheromones has not stopped some enterprising individuals from trying to make money from love potions claiming to contain human pheromones. In reality, these products often use pig or deer pheromones.
Human pheromones are an important concept in pop culture, where it is suggested that they can have a significant influence over the human ‘mating ritual’, similarly to that of animals.
As mentioned in the screencast, androstenone is a steroid which has a musk-like odour and is found in human sweat, human urine and in the saliva of pigs. Androstenone is often called a pheromone and can sometimes be found in ‘love potions’, where sellers claim its addition will increase female libido and the attractiveness of men. Despite many years of work, there is no evidence to suggest that humans experience the effects of pheromones the same way other animals do, but that doesn’t stop people from buying these so-called ‘love-potions’ and even attending Pheromone Parties.
The idea of a ‘Pheromone Party’ is as follows: unwashed t-shirts are put into numbered bags and these t-shirts are then sniffed by others. If the odour of an unwashed t-shirt is found to be appealing, a potential date between the sniffer and the owner could occur. A gathering of this type occurred first in 2010 in Brooklyn, New York, gaining much success, and then spreading to Los Angeles and London. The people attending these parties hope that, by using their sense of smell, they will be able to use the ‘Pheromone Party‘ to find love.
Interestingly, research has shown that women have keener senses of smell than do men (this may be due to having more cells in the olfactory bulb – the part of the brain responsible for the sense of smell), that men’s body odours are harder to cover up than are women’s, and that women’s brains respond differently when smelling sweat samples from men who were sexually aroused and men who weren’t.

Some questions to ponder

Does anything in your experience cause you to believe that humans might have pheromones? Do you think that pheromone parties are truly able to help someone find an appropriate mate, just like pheromones in animals?

Armpit chemistry

Researchers at York and Unilever have pinpointed the bacteria that is the main offender in making armpits pungent – the culprit, Staphylococcus hominis, acts by breaking down naturally secreted sweat compounds into smelly compounds including thioalcohols (e.g. CH3CH2CH2C(SH)(CH3)CH2CH2OH). Going forward, the team envisage a deodorant that would prevent armpit bacteria from producing thioalcohols rather than simply killing them off, as typical deodorants do.
Related to this, has anyone tried using a probiotic deodorant? These recently introduced underarm salves claim to use a healthy mix of bacteria to combat body odour – bacteria from non-smelly armpits are used to eradicate ‘bad’ bacteria in stinky armpits.

Can we smell fear?

We have seen that guard bees release alarm pheromones to alert others to a threat, so what about humans? As yet, no one has identified a compound in human sweat that corresponds to our level of anxiety. However, a number of experiments indicate that sweat born from emotion (e.g. on watching a scary film) has a different smell to sweat from exercise. For example, in 2002, a study of 60 women rated sweat from women who had watched a scary movie as stronger, less pleasant and smelling more “like aggression” than sweat from women who had watched a neutral movie. For such studies, it can be difficult to find volunteers willing to forego deodorants for several days and it bodes the question, bearing in mind the fragrances we daily dab onto our bodies, would any signals that sweat might contain be detectable?
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Exploring Everyday Chemistry

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