The Scent of Truth: The Mystery of Human Pheromones

Do human pheromones really exist?

Reviewed by Tyler Woods

Key points

• Human pheromones have been a hot topic for decades, but solid evidence is still scarce.
• In 2023, researchers found that women’s tears carry a protein that can significantly reduce aggression in men.
• There are many more chemicals in our body’s secretions waiting to be tested for pheromone-like effects.

My friend Marty was absolutely convinced that humans give off pheromones. She swore up and down that one time, on a crowded bus, she accidentally bumped into a stranger and was suddenly, inexplicably, drawn to him. “It must be the pheromones!” she declared, cocky as ever, and then laughed. “I even followed him for a few blocks.”

Showing that humans use pheromones, however, is a lot harder in science. One of the first attempts came from Martha McClintock, then a student at Wellesley College. In the late 1960s, she noticed that while her dormmates had different menstrual cycles at the start of the semester, by the end of those three to four months, their periods had magically synced up. There had to be a pheromone for that effect, she inferred (1).

But where exactly is this mysterious pheromone hiding? Some guessed the armpit—nature’s little chemical factory. The problem? The armpit churns out a whole cocktail of funky substances, so which one is the guilty party? Could it be 3M2H (short for (E)-3-methyl-2-hexenoic acid), the main ingredient behind that “delightful” scent we call human sweat?

I was itching to test the idea, but I never got around to it. Getting my hands on the chemical wasn’t the issue—you don’t have to go scraping armpits to collect it. A quick lab synthesis, a few days of work, and voilà! But testing its effects on enough women? Now, that was the real hurdle.

Lucky for me, I had Wendy Williams, a sharp psychologist, and Corinna Avelos, a pre-med powerhouse, on my side. Together, we ran a double-blind experiment with dozens of young, heterosexual women volunteers. Their nightly ritual? Dabbing their upper lips with rubbing alcohol—either plain (our control) or spiked with an unperceivable dose of 3M2H (10 ppm)—just before bed. For four months, we tracked their progress with painstaking detail. Finally, 16 of our dedicated volunteers made it to the finish line, and the moment of truth arrived. The big reveal? Drumroll... nothing. A big fat statistical zero! So much for the grand, life-altering effects of 3M2H (2).

Did we just lose our scientific bet, or was our sample size simply too small to catch the action? It’s hard to say. But one thing’s clear: plenty of other studies have struggled to replicate McClintock’s findings. Critics have pointed fingers at everything from statistical slip-ups to pure chance. And just like that, the groundbreaking “first evidence” of human pheromones starts to look shaky.

But in 2023, a fresh discovery reignited the flickering hope for human pheromones. In a study led by Shani Agron, researchers managed to collect 149ml (about two-thirds of a cup) of emotional tears from six women known for their “easy crying” skills. They then had male volunteers take a whiff. The results? Astonishing. The neural link between aggression and smell lit up, testosterone levels plummeted, and male aggression dropped by a staggering 43.7 percent. They even pinpointed four olfactory receptors in our noses that latch onto the magic aggression-taming protein in women’s tears (3). With evidence this solid, the idea of human pheromones starts to feel more like fact than fiction.

A new research article, authored by my long-time collaborator Jianxu Zhang and his team at the Chinese Academy of Sciences, reveals a wide array of chemicals from human sweat glands alone that could potentially broadcast who we are—our individuality, gender, sex, emotion, physiological state, and reproductive status (4). Most of these chemicals haven’t undergone the same rigorous testing as those linked to menstrual synchronization or aggression reduction. So, there’s plenty of room for more thrilling research on human pheromones in the future. Stay tuned!