The notion that humans may communicate through chemical cues known as pheromones has fascinated researchers for more than half a century. The concept, well established in animals, has spurred decades of studies attempting to work out whether similar mechanisms operate in people.
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In the animal kingdom, pheromones are uncontroversial. Ants rely on scent trails to navigate, dogs use chemical markers to define territory, and moths disperse airborne compounds to attract mates. Whether humans use comparable signals, however, remains a far more complicated question. Could someone genuinely provoke a physical or emotional response in another person without their awareness? And might such cues influence attraction?
Despite more than 60 years of investigation, firm evidence remains scarce – though recent discoveries suggest scientists may be inching closer. In 1959, Adolf Butenandt and his colleagues identified the first known pheromone, bombykol – a chemical produced by female silkworm moths to draw in males. Soon afterwards, researchers adopted the term ‘pheromone’ to describe any chemical released by one member of a species that triggers a specific reaction in another.
This breakthrough sparked an extensive search for human equivalents. One of the earliest high-profile claims emerged in 1971, when Martha McClintock published research suggesting that the menstrual cycles of 135 women living in the same university dormitory appeared to synchronise over time. The so-called McClintock effect was widely heralded as proof of a human pheromone, but subsequent attempts to replicate the finding failed, and statisticians later showed that apparent synchrony can occur by chance.
Over the years, scientists have homed in on four chemical candidates: androstenone, androstenol, androstadienone and oestratetraenol. These compounds have been linked to social perception, mood or attraction, yet none has been robustly demonstrated to behave like a true pheromone. Many studies rely on doses far exceeding natural levels, while others suffer from weak experimental design and inconsistent data, leaving the evidence inconclusive.
One of the field’s most famous experiments – Professor Claus Wedekind’s 1995 “sweaty T-shirt study” – invariably emerges in discussions of human scent signalling. In this experiment, women were asked to rate the odour of T-shirts worn by men. Those not using the contraceptive pill tended to prefer the scent of men whose immune system genes, known as MHC genes, differed most from their own. Evolutionarily, this preference makes sense: pairing with a mate who has complementary immune genes may increase offspring resilience to disease.
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Although the study has been replicated and is often cited as compelling evidence of human chemosignalling, it does not meet the strict definition of a pheromone. Human body odour is a complex mixture, shaped largely by bacteria on the skin, and tends to influence conscious preferences rather than triggering automatic biological responses.
Nonetheless, some scientists believe the search is far from futile. Among them is Dr Tristram Wyatt, Senior Research Fellow in the University of Oxford’s Department of Zoology, who has spent decades examining how pheromones evolve. He argues that, viewed as another animal species, it would be surprising if humans lacked pheromones entirely. Human body odour, for example, becomes more pronounced at puberty – a time when, in many species, scent signals begin to carry reproductive significance.
But identifying a human pheromone is exceptionally challenging. Humans emit thousands of volatile molecules, making it arduous to identify the one responsible for a specific effect. Reactions to smell are further shaped by personal experience, culture and emotional state, complicating attempts to measure consistent behaviour. Wyatt notes that, without a reliable bioassay – a clear, measurable response to a scent – pinpointing a pheromone is nearly impossible.
Reproducibility has also been an obstacle. Many early studies had small sample sizes and lacked rigorous controls, while publication bias favoured positive findings, creating an impression of stronger support than truly exists.
Despite the setbacks, Wyatt is encouraged by a promising French study investigating secretions from the areolar (Montgomery’s) glands of breastfeeding mothers. When newborn infants were exposed to the scent of these secretions, they instinctively turned their heads and displayed suckling behaviour, even when the scent came from a woman who was not their mother. Wyatt describes this universal, automatic response as the most compelling lead yet in the hunt for a human pheromone.
Another intriguing development emerged in 2023, when researchers at the Weizmann Institute of Science in Israel examined the effect of tears shed by women who had watched a sad film. Men who smelled the tears showed reduced testosterone levels and distinct changes in brain regions linked to aggression and smell. Scientists also identified four nasal receptors capable of detecting the chemical signal. Work is now under way to isolate the specific molecules responsible, which could, in theory, be developed to help reduce aggressive behaviour. Still, despite growing evidence that smell plays a meaningful role in human social and sexual behaviour, a genuine human pheromone has yet to be proven.
Wyatt argues that progress will require carefully designed, large-scale studies and a move away from repeatedly testing the same unverified compounds. “Only rigorous, evidence-based research will give us real answers,” he says. “The search for a true human pheromone has only just begun – but with the right approach, we may finally be heading in the right direction.”
