Answering the question of why humans are the only species that visibly cry from grief or frustration may hold the key to reducing aggression in high-stress environments, such as prisons or police interventions, without the need for sedation.
This, according to research conducted by neuroscientist Noam Sobel and colleagues at the Weizmann Institute of Science, which argues that women’s emotional tears carry a chemical signal capable of reducing male aggression by roughly 44%.
The idea to study tears didn’t arise spontaneously. For decades, researchers have examined pheromones in lab mice to explain patterns of coordinated social behavior involving sex, status, and safety. These studies revealed that bodily fluids in rodents do much more than eliminate waste or lubricate eyes—they carry peptides that alter behavior, making airborne chemical cues a key factor in rodent social order.
In particular, studies found that tears in juvenile mice inhibit sexual behavior in adult males, that female mouse tears suppress inter-male aggression, and in blind mole rats, that pheromones secreted near the eye act as a “please don’t attack me” signal during social encounters.
This body of research gave scientists a ready-made hypothesis: if rodent tears influence behavior, human emotional tears might transmit similar chemosignals. Sobel’s team followed this line of inquiry with a series of tests examining whether women’s tears—produced through exposure to sad or emotionally distressing stimuli—could influence men’s behavior in a controlled setting, and perhaps shed light on why humans cry at all.
This led to Sobel’s initial 2011 study that revealed how sniffing women’s emotional tears lowered men’s testosterone and sexual arousal. Then, in 2023, they returned to the lab to explore whether those same tears could dampen male aggression.
The three-party study included 25 men in their mid-twenties to sit and sniff tears donated by six women aged 22-25 who could cry on demand while watching sad films. Participants were asked to sniff jars containing the tears or saline collected from the women’s cheeks. The order was randomized, and the men were told only that they were smelling “very weak odors,” not that any of the jars contained human tears.
Afterward, the men’s aggression was measured as they played a game that awarded money before it occasionally “stole” it back, leaving the men with a choice to keep paying and earning or deduct money from opponents purely out of revenge. Point Subtraction Aggression Paradigm (PSAP) tests are standard lab measures of reactive aggression that allow researchers to quantify aggression as the ratio of revenge responses to provocations.
In instances where saline was used, the men consistently produced a baseline aggression score. By contrast, when women’s emotional tears were used, their aggression scores dropped by an average of 43.7%. The finding not only demonstrates that men’s olfactory systems can detect female chemosignals, but that the effect is strong, nearly cutting reactive aggression in half. Of the 62 olfactory receptors tested, 21 showed signs of activation when exposed to tears, with four demonstrating a clear dose-dependent response while ignoring saline. Connectivity analyses further suggested a plausible neural pathway linking the nose, olfactory cortex, and aggression circuits, with increased activity in brain regions involved in smell and socio-emotional processing.
While the study was relatively small in scale, Sobel and his team’s findings offer some of the strongest evidence yet that human tears function as chemical signals that can influence human actions such as aggression. Beyond hinting at an evolutionary explanation for why humans are the only species known to cry emotional tears, the research opens the door to both intriguing—and controversial—applications.
For instance, tear-derived compounds, once isolated and synthesized, could be used as de-escalation tools in prisons or for riot control. Other applications may include their integration into workplace design for high-risk occupations like firefighting, deployment in psychiatric settings, use in crowd control, or incorporation into therapies for anger management or domestic-violence rehabilitation. Such technologies might even be commercialized for consumer wellness.
Yet the implications of the team’s research, published in PLOS Biology, are fraught as well. A chemical that can influence aggression without a person’s knowledge raises profound ethical questions. Such compounds could shape more than behavior—they could affect consent, governance, and, fundamentally, raise significant questions about who has the authority to control or deploy any tool that can alter emotional responses—even if that involves suppressing aggression.
Marie Nicola is a journalist, pop culture historian, and former CBC Senior Producer whose investigative research explores the intersection of culture, technology, and history. She has contributed to the Globe and Mail, collaborated with Reddit, and been featured in TrendHunter as an early innovator in streaming and digital broadcasting. Follow her on X @karmacakedotca.