A Sniff of Universal Love

I close my eyes and let my nose guide me. The smell of ink, the buttery scent of the pain au chocolat I am having for breakfast, and the pungent aroma of my neighbour’s dieting broth float by the odorant receptors lining the nasal cavity above and behind my nose. The information about the types of molecules they detect is then passed to the nerve cells in the olfactory bulb, a brain structure responsible for forming a map of all the odours I have ever sniffed.

What if my relationships with odours were not so superficial? I could name all the vegetables that are in the broth and distinguish the smell of hands which cut the ingredients, the odour of the dog which brushed its tail along the shopping bag they were in… Jean-Baptiste Grenouille, a character from the book Perfume: The Story of a Murderer, written by Patrick Süskind, had a supernatural ability to tell apart a myriad of smells. As every human being possesses a chemical signature or odourprint consisting of a bouquet of aromas, Grenouille’s nose could detect people in a radar-like fashion. Strangely, Grenouille himself did not have an odourprint, he alienated almost everyone he met and the outcast status fuelled his hate towards humanity. He murdered twenty five beauties and distilled their bodily scent to create a perfume that made everyone fall in love with him.

Grenouille lived in the 18th century Paris, but what if he was a crazy chemist polishing his master plan in a 21st century lab? Can science provide the means for wooing the world? The key ingredient of the perfume could have been a powerful combination of pheromones, a class of species-specific odorant molecules that convey messages from one individual to another and are widely used across the animal kingdom. The first molecule classified as a pheromone in 1950s was bombykol, a crucial compound in the mating rites of silk moths. Ever since then, this term has been used with an erotic undertone. A few decades ago, it was assumed that these attractants occur only in insects, because mammalian smells form signatures that are too complex to be labelled as pheromones. However, recent studies have shown that mammalian pheromones tend to hide in the clefts of bigger molecules which form a part of the animal’s odourprint.

Although the interaction between bacteria and skin secretions in the armpits yields some volatile compounds that are assumed to be pheromones, human-specific attractants have not been identified for certain. Not surprisingly, some internet companies have decided to ignore the scarcity of scientific data and consider that dismal love lives can be spiced up by a droplet of copulins pour la femme, or androstenones pour an insecure homme. Experiments with rhesus monkeys showed that copulins from vaginal secretions help the females turn on potential mates, but are useless for the members of Homo sapiens. Androstenone from male sweat seems to be more promising as high experimental concentrations of this chemical can stabilize menstrual cycles of women and therefore increase their chances of pregnancy. Unfortunately, the magic ends when milder doses are applied. The first compound with an official ‘human pheromone’ status might be an as yet unidentified molecule that synchronises menstrual cycles in a group of females that live together, for example, in all-girls dorms.

Exploring the detection mechanisms of human pheromones is as challenging as the identification of these molecules. Humans, like most other mammals, should be able to detect pheromones through their vomeronasal organ (VNO), located in the front part of the nose. However, the odorant receptors of the human VNO do not function and the genes responsible for creating connections between the organ and the olfactory bulb are inactive. This does not mean that the story of human pheromones is over: experiments with mice have proved that the mammalian nose can manage without a functioning VNO because some pheromones are detected by the ‘ordinary’ odorant receptors along with the other smell molecules that come their way.

Another issue to consider is the universal nature of Grenouille’s perfume. Even if scientists managed to extract potent pheromones from human sweat and applied them to the love-thirsty individuals, the potion would not work on everybody. When it comes to dating, our preferences are influenced by a large region in our genome called major histocompatibility complex (MHC) which has an important role in the immune system. A variety of MHC genes between the two partners could lead to children who are better protected against diseases. Interestingly, the old saying that ‘opposites attract’ may not be true: couples prefer moderate, not maximal differences between their MHCs.

Even though Lynx adverts tell us a different story, the creation of a strong attractant is not biologically plausible yet, and there is no need to rush into it. Grenouille’s perfume drove people to ecstasy, but their admiration left him unmoved. If spraying a chemical could guarantee a never-ending row of one night stands, would you try it out?


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