Decades of research have failed to yield any human pheromones.
© LOUIE PSIHOYOS
By Kai Kupferschmidt
CHICHELEY, U.K.—Jonathan Williams mostly studies the molecules that oceans and rainforests give off into the atmosphere. He’s an unlikely recruit to a new cause: rescuing the decadeslong search for a human pheromone—a chemical signal in human body odor—from the doldrums. Williams, who is at the Max Planck Institute for Chemistry in Mainz, Germany, joined two other atmospheric chemists here last week at a small Royal Society meeting on chemical communication in humans to describe how their workhorse technique for studying trace chemicals in the atmosphere, proton transfer reaction mass spectrometry (PTR-MS), could aid the pheromone hunt. “It really feels like we are on the brink of something great,” says one of the meeting’s organizers, psychologist Craig Roberts of the University of Stirling in the United Kingdom.
Something great is what the field needs. Since 1959, when German biochemist Adolf Butenandt isolated the first pheromone—a compound named bombykol that female silkmoths use to attract partners—generations of researchers have looked for similarly powerful chemicals in humans. But they haven’t identified a single one. The few high-profile claims, for example that women living together synchronize their menstrual cycle through chemical signals, have not stood the test of time. “The field is in a bit of a crisis,” says Andreas Natsch, a researcher at the fragrance company Givaudan in Vernier, Switzerland.
Part of the reason is that it’s a small field with relatively little funding. “Smell is the Cinderella of human senses,” says zoologist Tristram Wyatt of the University of Oxford in the United Kingdom, who has written a textbook on pheromones. Past studies often used small numbers of volunteers and questionable statistical methods. And then there is the sheer complexity of the subject. The human body emits hundreds of volatile compounds. Most pheromone studies give no more than a snapshot of them, for instance by asking participants to wear a T-shirt for a night or putting pads under their armpits and then analyzing captured compounds with a mass spectrometer.
By contrast, PTR-MS—which works by transferring a proton to volatile compounds in the air and then analyzing their mass from how they move in an electric field—is more like producing a video; it allows researchers to measure compounds in real time and to identify those that change in abundance after a certain type of stimulation. “You can eliminate a lot of hay from the haystack we have been searching through,” Roberts says.
Williams glimpsed the technique’s potential years ago, when he analyzed the air around soccer fans during a game at a stadium in Mainz. “We could follow people’s behavior by following the chemicals they emitted,” he says. For instance, acetonitrile, a component of smoke, peaked at half time, when many people lit up a cigarette.
It really feels like we are on the brink of something great.
Williams wondered what the chemical signature of the euphoria after a goal would look like. That match, however, offered no joy, as it ended with a 0-0 score. To avoid another disappointing outcome, Williams turned to a local cinema instead. He found not only that crowds watching funny and suspenseful movies generate different chemical signatures, but also that the emissions change with plot twists. “In The Hunger Games, you could tell exactly when the heroine starts the big showdown fight,” Williams says. In a paper in Scientific Reports, he reported that carbon dioxide levels increased, probably as the audience breathed faster; so did isoprene, which could be given off by twitching muscles.
Another atmospheric scientist, Ben Langford at the Centre for Ecology & Hydrology in Edinburgh, was so intrigued by the work that he decided to team up with Roberts, who was excited to learn about PTR-MS. Langford says: “It was almost like I was handing him a key to a door he had always wanted to open.” In studies that they are preparing for publication, the duo has been showing movie clips to volunteers while analyzing the air under their armpits. They have identified some compounds that change in abundance during frightening scenes and plan to investigate further; whether the molecules constitute an actual chemical signal, however, is still unclear.
That study joins other work focusing on fear or aggression—a change after many years when pheromone research has searched for signals linked to sexual attraction and mate choice, which some now think may be harder to find. (“It used to be all about love and now in the age of [U.S. President Donald] Trump fear and aggression are the important topics,” Natsch says.) In one ongoing study presented at the meeting, scientists collect sweat from Israeli soldiers before their first parachute jump and compare it with sweat collected in a different setting. Such extreme, life-or-death situations might present the best shot at identifying a chemical signal, Roberts says.
That signal may well turn out to be not a specific “fearomone” but a complicated series of changes in the abundance of several compounds, just the kind of thing Williams and his colleagues are accustomed to tracing in the atmosphere. That his new field is less mature than atmospheric chemistry only makes it more attractive, Williams says: “There is such an opportunity for discovery here.”
Source: Science Mag