Explainer: the science behind pheromones

In the 1870s French entomologist Jean Henri Fabre showed for the first time that it was smell, not sight, or sound, which guided male moths in search for females. It still took another 80 years or so for the first pheromone to be isolated and synthesised.

And no, the researchers did not identify a heart-palpating human pheromone. More on that below.

In 1959, Nobel Prize-winning German biochemist Adolf Butenandt and colleagues identified the sex pheromone they called bombykol, which is produced by female silkworm moths to attract males of the same species.

Bombykol molecule
Bombykol molecule. Credit: MOLEKUUL/SCIENCE PHOTO LIBRARY/Getty Images

What are pheromones?

Pheromones are chemical signals secreted by organisms for communication, usually between members of the same species. They’re typically secreted by specialised glands or tissues.

Pheromones are smells, but importantly not all smells are pheromones; a pheromone may consist of a single chemical, or a mixture, and it must induce a specific physical reaction in the individual receiving it.

There are two kinds of pheromones: releasers and primers. Releaser pheromones trigger an immediate effect on the behaviour of the recipient, whereas primer pheromones affect physiology and produce an effect on behaviour after a period of time.

Alarm pheromones in social insects like ants, bees, wasps, and termites are releaser pheromones. When a bee stings, it’s the release of a pheromone from a gland near the stinger that stimulates others to rush to the site and start stinging too.

In mammals, primer pheromones are important in coordinating reproductive physiology. For instance, in mice, exposure to pheromones in the urine of adult males causes immature females to sexually mature more quickly.

These effects aren’t learned, they’re innate.

How are they detected?

In some animals pheromones can be detected by pheromone receptors in the two olfactory systems. The main olfactory system is the one that detects airborne odours and then many mammals, all snakes and lizards, and some amphibians, have an extra olfactory organ, the vomeronasal organ (VNO), which detects heavier, moisture-borne odours.

In insects, the primary sensory organs are the antennae and maxillary palps which contain sensory organs called sensilla.

Once these chemosensory signals are detected, the information can then relayed different behavioural centres in the brain.

For example, pheromones can be important for interactions between parents and their offspring; female rabbits release a mammary pheromone that causes newborns to search for and latch onto a nipple within just three to five seconds!

In bacteria, chemical signalling using pheromones is important for eliciting coordinated responses within bacterial communities – like biofilm formation and dispersal.

Do humans produce pheromones?

Unfortunately for the perfume manufacturers boasting pheromone-infused fragrances that make you irresistible, findings from studies of potential human pheromones have been extremely inconsistent.

To date, scientists haven’t been able to definitively identify any human pheromones.

To do so would have to involve isolating a single molecule, or combination or molecules, that are present in all male or all female humans, and which produces a reliable behavioural or physiological effect on other people.

Unfortunately, it’s not easy to identify influences on human behaviour given our cultural complexity and diversity, and studying smell is difficult because odours are invisible and hard to control.

Four specific substances have been the main subjects of research over the decades: testosterone-derived androstenone, androstenol, and androstadienone, and the oestrogen-derived oestratraenol. But according to a 2015 review “there is no bioassay-led evidence for the widely published claims that four steroid molecules are human pheromones.”

Common problems with the studies include small sample sizes, an overestimate of effect, positive publication bias (where the outcome of the research biases the decision to publish) and lack of replication. 

But just because we haven’t found them yet, it doesn’t mean that human pheromones don’t exist. Some scientists believe that the most promising lead is a nipple secretion from the areola glands of lactating mothers. It causes a baby, any baby, to open its mouth, search for a nipple, and suckle.

We haven’t yet identified the specific molecule or combination of molecules that causes this effect. But who knows? Maybe one day we’ll be able to bottle it up to help those who struggle to breastfeed.

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