Sex, sweat and genes

Do we use pheromones to find a mate?

The music pounds, glasses clink. Tonight is a night many are on the prowl, hoping to hit it off with someone and find a love interest. However, this isn’t your average Wednesday night at The Lash (never YOLO): nobody is approaching anyone based on their fantastic dance moves or that gorgeous smile. Instead, people are picking up sweaty t-shirts and inhaling their scent.

Pheromone Parties are a Los Angeles sensation catching on in the UK. Smelly BO has been rebranded with people now speaking about sexy ‘pheromones’. The party organisers claim that body odour communicates information to potential partners, and underlies what many describe as “chemistry” between individuals. That is, an underlying sexual attraction where you cannot put your finger on the cause. Prior to the event you must sleep in an unwashed t-shirt for 3 days without deodorant. T-shirts are then numbered, with only you knowing your own digit. The t-shirts are then laid out and individuals go forth and sniff l’eau de BO. If you find the smell attractive, you take a photograph with the numbered t-shirt. The results are compiled and at the end individuals who have provided the preferred t-shirts are encouraged to approach you and voila: chemistry and a match made in heaven (apparently). This sounds like a fantastic gimmick, but there has actually been a lot of research undertaken into whether humans use pheromones in sexual selection.

Manfred Milinski, Director of the Max Planck Institute for Evolutionary Biology, has studied the influence of odour on mate choice for over two decades. And all fingers point towards our immune system. The major histocompatibility complex (MHC) is a genetic region that produces molecules used in our immune response. These ‘immunogenes’ produce molecules that discriminate between ‘self’ protein fragments, known as peptides, which are produced by our own body, and foreign ‘non-self’ peptides that could potentially be pathogenic. Found in all animals with a backbone, MHC molecules will identify ‘non-self’ molecules and mark them for destruction by our immune system. But what does this have to do with perspiring armpits?

In addition to discriminating between proteins, Milinski argues that the MHC can be used to discriminate between people through the medium of smell, in order to find a mate with a dissimilar MHC. The MHC is a highly varied genetic region, meaning that there are many different versions of these MHC-produced molecules within a population. Milinski explains: “We preferentially choose a partner with a dissimilar set of genes. There is evidence that offspring with genetically distinct parents have a robust immune system. If you have a child with a diverse range of MHC genes, they will be able to fight off a diverse range of pathogens.”

This mechanism of mate choice was discovered in mice over 30 years ago, where they preferentially mated with those that had a dissimilar MHC. Mice convey their personal odour identity (termed an odourtype) via MHC molecules found in urine. This odourtype will represent the genetic identity of the mouse. As humans and mice have a very similar MHC region, it posed the question of whether we also use this mechanism. While humans certainly do not share the urine sniffing behaviour associated with mice, perhaps the Pheromone Parties are on to something – we may be communicating an odourtype to potential mates.

Claus Wedekind, now at the University of Lausanne, hypothesised that our odourtype was communicated through our sweat. The experiment he conducted was similar to the Pheromone Parties: people slept in a t-shirt for two consecutive nights and individuals of the opposite sex then rated how attractive the t-shirt smell was. All participants had their MHC genes determined, with the experiment demonstrating that people preferred the smell of individuals who had a dissimilar MHC to their own. However, the human genome is incredibly complex; regions other than the MHC could also be influencing olfactory mate choice.

This issue was addressed by Raphaelle Chaix. Using data from genomic databanks, which store the entire genetic region of many individuals, they compared how similar the MHC region was between married individuals relative to similarities across the rest of the genome. This determined that the MHC genetic region in spouses was significantly more dissimilar than the rest of the genome. Therefore, we can conclude that body odour may indeed be important in mate choice. However, if our natural smell is really so important, why is the global perfume industry worth £18 billion?

Many cultures have valued perfumes over the centuries: Tudors carried around perfumed balls stuffed with aromatic spices, whereas Ancient Egyptians preferred to rub musky oil over their bodies. However, finding a scent you like could be more important than simply smelling nice. A study by Milinski and colleagues discovered that individuals with specific MHC genes prefer to wear specific perfumes. While deodorant masks perspiration and the smells associated with it, your favourite perfume will instead complement body odour, highlighting your natural scent.

While research has supported the argument that smell is used for communication between potential partners, we cannot ignore other important factors involved in choosing a mate. People often have their own tastes for personality and physical traits, be it desiring someone with bulging biceps or fancying the class clown.

Whether it is the novelty factor or if people are seriously considering this research field, there is a developing market for using these MHC-produced olfactory cues in matchmaking. In addition to Pheromone Parties, websites like Lovegene are offering a fresh approach to online dating. Your MHC region is genetically determined and then search through an online database of individuals, where it shows how dissimilar their MHC region is to yours. The founder, Laurynas Piliuskys, claims: “People can lie about their images, personality and other biographical information. But with genetics you can’t fake it! You are what you are.”

If you are frequenting Tinder and OK Cupid, you may want to think twice about how liberally you apply your deodorant – especially if you are going to Pheromone Party later in the evening.

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