When we cry, we may be doing more than expressing emotion. Our tears, according to striking new research, may be sending chemical signals that influence the behavior of other people.
The research, published on Thursday in the journal Science, could begin to explain something that has baffled scientists for generations: Why do humans, unlike seemingly any other species, cry emotional tears?
In several experiments, researchers found that men who sniffed drops of women’s emotional tears became less sexually aroused than when they sniffed a neutral saline solution that had been dribbled down women’s cheeks. While the studies were not large, the findings showed up in a variety of ways, including testosterone levels, skin responses, brain imaging and the men’s descriptions of their arousal.
“Chemical signaling is a form of language,” said one of the researchers, Dr. Noam Sobel, a professor of neurobiology at the Weizmann Institute in Israel. “Basically what we’ve found is the chemo-signaling word for ‘no’ — or at least ‘not now.’ ”
The researchers are currently studying men’s emotional tears, so the scientific implications of, say, the weeping of the new House speaker, John A. Boehner, remain an open question. But Dr. Sobel said he believed that men’s tears would also turn out to transmit chemical signals, perhaps serving to reduce aggression in other men.
Dr. Sobel said the researchers started with women because when they advertised for “volunteers who can cry with ease,” they could not find men who were “good criers,” readily able to fill collection vials. Fortunately, he said, “we have a male crier now.”
Several experts said the findings — besides potentially adding subtext to crying songs through the ages, from Roy Orbison to the Rolling Stones — could be a first step toward a breakthrough on a mysterious subject.
The discovery of a chemical signal in tears suggests “a novel functional role for crying,” said Martha K. McClintock, a professor of psychology at the University of Chicago who is known for her work on pheromones and behavior. “It really broadens the possibilities of where signals are coming from.”
Robert R. Provine, a psychologist and neuroscientist at the University of Maryland, Baltimore County, who has studied crying, said the discovery was “a really big deal” because “emotional tears are a very important evolutionary development in humans as a social species,” and this “may be evidence of another human pheromone.”
Many questions remain, including whether the results can be replicated by other researchers, what substance could comprise the chemical signal and whether it is perceived through the nose or another way.
Why women’s tears would send a message of “not tonight, dear” is puzzling. Some experts suggested the tears could have evolved to reduce men’s aggression toward women who are weakened by emotional stress. The studies did not measure the effect on aggression, although future research might, Dr. Sobel said. Another thought, he said, is that the effect of tears evolved in part to coincide with menstrual cycles.
“There’s several lines of evidence that women cry much more during menstruation, and from a biological standpoint that is not a very effective time to have sex, so reducing sexual arousal in your mate at that time is really convenient,” he said.
Dr. McClintock, who reported 40 years ago that women who lived together tended to synchronize their menstruation, objected. “Oh, please,” she said. “Do we know that women cry more often during menstruation?”
She said it was “premature to speculate about the evolutionary function” of chemo-signaling in tears, adding: “I have no doubt that it affected sexuality as they report, but I would be very surprised if it doesn’t turn out to affect other emotions in other contexts. Maybe it’s affecting some deeper, more fundamental psychological process that drives the effect that they’re reporting.”
The researchers accidentally happened upon the evidence that women’s tears make men feel as if they have taken a cold shower.
They had assumed chemical signals from tears would trigger sadness or empathy in others. But initial experiments found that sniffing women’s tears did not affect men’s mood or empathy, but “had a pronounced influence on sexual arousal, a surprise,” Dr. Sobel said.
Deciding to investigate more rigorously, the researchers posted fliers on several Israeli college campuses seeking easy criers. Seventy women volunteered, along with one man. But of the 70 women, there were only six “who were really good” at bawling their eyes out, Dr. Sobel said. They became the researchers’ “bank of criers”; a stable of “backup criers” was kept in reserve.
“We had to use fresh tears,” no more than two hours old, Dr. Sobel said, and frozen would not do. So the criers were called on frequently to sob a renewed supply, a milliliter each time. The women, who were in their late 20s and early 30s, watched scenes from Hollywood tear-jerkers like “My Sister’s Keeper” and “When a Man Loves a Woman” and one from Israel, “Broken Wings,” said Yaara Yeshurun, a doctoral student on the team. Ms. Yeshurun was also one of the criers, losing it over “Terms of Endearment."
As a control, researchers trickled saline down the women’s faces, also collecting that in vials. Tears and saline were dribbled onto pads that were then affixed below men’s nostrils to approximate a hug with a teary woman. The men, in their late 20s, each sniffed tears one day and saline another day, without knowing which was which.
In one experiment, tear-sniffing made the men more likely to rate women in photographs as less sexually attractive. In another, to establish a context of sadness, men watched a scene from the movie “The Champ” after sniffing tears or saline. Sniffers became equally sad with both tears and saline, but tear-sniffers showed reduced sexual arousal and lower levels of testosterone.
Finally, the researchers turned to brain imaging. They showed men scenes from “9 ½ Weeks” — specifically the more explicit version that was shown in Europe, which, Dr. Sobel said, “has been validated as being particularly arousing.” Functional M.R.I. scans identified the men’s arousal in specific brain areas. Then they sniffed tears or saline and watched sad movies. The tear-sniffers showed less activity in the brain regions that reflected arousal.
The studies were financed by the Minerva Stiftung Foundation, a German group that supports research involving Israeli and German scientists, often with money from the German government.
Dr. Sobel, who also plans to study children’s tears, said the substance might be a protein or steroid, and is most likely perceived nasally. He also wondered if animals’ tears could have chemo-signaling effects; he cited a study showing that when blind mole rats washed their faces with tears, it reduced aggression in other males.
William H. Frey II, a biochemist who showed that the chemical composition of emotional tears is different from that of reflexive tears, like when peeling an onion, said he was “thrilled to death to see somebody doing something on the chemistry of emotional tears.” He said the results could be compatible with his theory that crying involves shedding stress-related toxins.
But Dr. Frey, director of the Alzheimer’s Research Center at Regions Hospital in St. Paul, said that more must be understood, including why sexual dampening would occur. Evolution may favor less sexual assertiveness toward a crying mate, he said, but if a woman’s tears are brought on by an attacker, “is a husband with less testosterone going to be more or less aggressive in defending his family?”
Still, Dr. Provine said the findings were “consistent with other proposed roles of tears, including solicitation of caregiving and reduction of aggression.” He added: “That tears are de-arousing would not be a surprise to most men. I can’t think of anything I’d rather do less than go see a tear-jerker.”
Dr. Sobel said whatever the evolutionary origin of emotional tears, he was not contending that his findings had modern romantic applications. “It’s not that I would recommend to any woman to cry to send a message,” he said. “It would be much better to just say no.”
