Out of the Shadows: I No Longer Believe in Human Pheromones

From my earliest fascination with animal behavior in college, through my pure sensory research phase at the Monell Center, and into my mercenary research phase in the fragrance industry, the question of human sex pheromones was never far from mind. Having studied sexual behavior and smell, I eagerly read the new studies and attended the promising talks hoping to see a definitive answer emerge. Curiously, as more research was done the case for human pheromones became more tentative. Researchers I knew and respected couldn’t even agree on basic physiological facts: do humans have a vomeronasal organ or not? If it exists is it functional? If it’s functional, does it deliver a behaviorally relevant message?

I grew increasingly impatient with this state of affairs. I wasn’t the only one seeking clarity: an endless parade of associate beauty editors, science reporters, and generally intelligent people asked me whether there was anything to the idea of human sex pheromones. The best I could offer them was the lame proposition that while the molecules and the means to perceive them might still exist, the effects of human sex pheromones were unlikely to be as dramatic as those in insects or rodents. This didn’t satisfy the associate beauty editors nor did it satisfy me. Reserving judgment in the face of conflicting data is a bedrock principle of science but it doesn’t make for good sound bites.

According to the definitions first developed in the early 1960s, a sex pheromone should trigger an invariant, reflex-like behavior in most people who smell it, and it should consist chemically of (ideally) one to (at most) a small handful of specific molecules. In theory, uncorking a sample tube of male pheromone ought to make women go gaga, while a nose full of female pheromone should make men go stiff, something along the lines of the wickedly clever story by Roald Dahl called Bitch.

So, thousands of studies and millions of research dollars later, where are we?

Richard Doty, a smell researcher at the University of Pennsylvania, has now supplied the book-length answer. In The great pheromone myth, Doty provides an exhaustive—and sometimes exhausting—account of the science behind mammalian pheromones. But this is much more than a summary of 50 years worth of research—it is a thorough and relentless examination of the evolving scientific claims made for the pheromone concept itself. And it is here that Doty has provided a major contribution: nothing less than an complete take-down of human pheromones.

The great pheromone myth is an argumentative tour de force. Like a skilled prosecutor cross-examining witnesses, Doty sets the trap by quoting researchers themselves as he reviews the definition of pheromones. From one scientist to the next we find inconsistencies, contradictions, and special pleading. The cumulative effect is devastating: it demonstrates the intellectual incoherence surrounding the term. A pheromone is a simple chemical—except when it’s a blend of chemicals. A pheromone has an innate releaser effect on other animals—except when learning or context is involved. Doty also quotes those who along the way cautioned about extending the pheromone concept from insects to mammals. Like a good courtroom lawyer, he plants seeds of doubt in the minds of jurors.

Doty spells out the technical shortcomings of animal and human experiments, but he always returns to his theme: that the results rarely meet the criteria for a pheromone, even as the criteria become ever more expansive and flexible. 

As Doty dismantles one pheromone claim after another, he also builds a powerful case for the behavioral and physiological effects mediated by body odors. Mothers recognize infants, infants recognize mothers, lover recognize each other—all through natural body scent. Many of these effects involve learning and the evaluation of context, even in rats. For example, “male rats exhibit an increase in testosterone and luteinizing hormone following exposure to the wintergreen-smelling odorant, methyl salicylate, when the odor had been paired with previous copulation.” Mice raised until weaning with artificially perfumed parents later prefer to mate with similarly scented mice; mice raised unscented prefer unscented partners. These results show the importance of smell in sexual behavior and speak to learning and adaptability; but they are hard to square with the idea that mammals respond only to pheromones composed of highly specific natural body scents.

To all of which one might reply, so what? So what if there is no solid evidence in mammals that meets the narrow technical definition of pheromones? What’s wrong with calling all these various effects pheromonal?

The problem is that the pheromone concept does no intellectual work. It provides no leverage for discovering new facts or phenomena. Pheromones are the intellectual version of elastic-waisted fat pants—the concept expands to accommodate each and every claim made for it. Once upon a time instinct theory was equally in vogue and used to “explain” all sorts of behavior. Today it’s rarely invoked. By specifying the roles of context and learning, behavioral science simply outgrew the need to appeal to instinct.

Today we are seeing a new wave of research by scientists such as Denise Chen, Bettina Pause, Johan Lundström, and others showing that body odors can transmit emotional state from one person to another, and can alter brain processing and hormonal levels. It’s clear that we are much more affected by the scent of other people than previously thought. The effects are many and varied; more will doubtless be revealed. But what is gained by shoving them all under the umbrella of “pheromones”? Very little, I believe. Like Doty, I’m pessimistic the public will ever give up its fascination with pheromones, but it’s time for scientists to file them away—right next to phlogiston—in the drawer labeled “formerly useful concepts”.