Ah, pheromones. Those airborne chemicals that cause your teenage students to become irresistible to one another. It’s a kind of animal instinct. Apparently. Just like when the female silkworm moth emits the sex pheromone, bombykol, the male begins to flutter his wings uncontrollably with excitement. He can’t keep himself away.

But what are pheromones - other than an excuse for students to behave inappropriately? They are molecules, or specific mixtures of molecules that give out a particular scent as a way to communicate with other members of the species.

For example, Japanese honey bees give off a specific attack pheromone when a giant hornet approaches, signalling the hive to swarm the hornet and roast it to death. Sounds harsh, but giant hornets can kill a honey bee every second to get to the nutrient-rich larvae they are looking for.

This brings us to another pheromones fact: they are adapted for their purpose. Attack pheromones tend to be small molecules, so they can dissipate through the air quickly and raise the signal, whereas pheromones for marking territory tend to be larger, less volatile molecules that will not evaporate away.

‘Teenagers definitely exhibit animal instincts’

So, what kinds of pheromones do humans have?

The answer is that scientists aren’t sure. There is no robust study that shows that human sex pheromones exist. However, pharmaceutical companies have played on the myth that certain molecules can increase sexual arousal for the last two decades. And their money, and persistence, have ensured that the story lives on.

One of the reasons why it seems likely that there is a human sex pheromone, is that humans get smellier during puberty. There seems to be a link between sexual maturity, and the secretion of small, volatile molecules. And teenagers definitely exhibit so-called animal instincts when it comes to sex.

But pheromones are universal. Species-wide. So, for a molecule, or a particular blend of molecules, to be a human sex pheromone, it needs to be linked to sexual behaviours, such as arousal, in all members of the species. This means that real human sex pheromones should look something like the “Lynx effect”: all the females of a species chasing some regular Joe simply because he smells so delicious.

Are pheromones to blame?

Wedekind’s famous “smelly T-shirt” experiment seems to contradict this.

The study asked men to wear a T-shirt for two days, and then women ranked the shirts according to how attracted to the smell they were. The study found that women were attracted to men with different major histocompatibility complex (MHC) genes to themselves. These genes encode immune responses, so the evidence suggests that men and women with different MHC genes may pair up to boost infectious disease immunity in their babies.

That’s all very interesting, but smells due to MHC genes are not pheromones - they are specific to each individual’s genetic material, not species-wide.

Can we blame pheromones for the way that teenagers behave, then? I’m not sure. All I can say about teenagers is that they are too young to be subconsciously worrying about the immune responses of their hypothetical children. So please make sure they wash properly after sport.

Emily Seeber is head of science at Bedales School in Hampshire

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