“We’ve identified that there is a chemosignal in human tears,” said Noam Sobel, a neuroscientist at the Weizmann Institute of Science near Tel Aviv. Sobel headed the study, which involved exposing men to tears collected in vials. It was published online Thursday by the journal Science.
Historically, tears have been of more interest to poets than scientists.
“Emotional tears” are considered by many biologists to be uniquely human. They’re known to have a different chemical composition than tears shed when the eye is simply irritated. The few studies of tears’ psychological effects suggest they have a help-soliciting function.
Whether the quenching of ardor is a big part of their evolutionary function or a side effect of a more complicated care-giving response isn’t known. But it now seems clear they contain substances that work unconsciously on others.
For practical reasons, Sobel and his colleagues have studied only women’s tears. But they suspect that men’s tears, and possibly children’s, also contain chemical signals and are eager to find out what messages they may convey.
“This experiment opened gazillions of questions. It opened way more questions than it answered,” Sobel said.
The new study places human tears in a family of fluids that includes urine and anogenital gland secretions.
Those fluids contain behavior-altering compounds, known as pheromones. Research in rodents has shown that liquids secreted from glands near the eye have a variety of social effects. In mole rats, they reduce aggressiveness in head-to-head underground confrontations. In mice, they stimulate aggression between males but promote mating behavior between males and females.
“What we have found is that human emotional crying may not be so unique after all,” Sobel said. “It is a reflection of something common to many if not all mammals, which is chemosignaling through lacrimal secretions.”
The study, which entailed collecting tears and exposing people to them in a laboratory, was greeted positively by the small circle of researchers who study crying.
“It’s the first report. I think it’s quite interesting,” said Robert R. Provine, a psychologist and neuroscientist at the University of Maryland Baltimore County, who has studied tears as visual cues.
“The results indeed are fascinating,” said Ad Vingerhoets of Tilburg University in the Netherlands, who has studied social reactions to crying. However, he said, he suspects that tears’ pheromones may have a bigger effect on another hormone, oxytocin, which is associated with social bonding, than on testosterone. He said he hopes further research will head in that direction.
In the study published Thursday, Sobel and his colleagues collected tears from women who cried after watching a sad scene in a movie. The researchers had previously trickled a saline solution — salty water — down the women’s cheeks and collected it as a “control” substance. Men were exposed to the two liquids, sniffing them in vials and, for some of the experiments, having a small pad soaked with the liquid taped between the nostrils and upper lip.
The men were unable to distinguish the two liquids; both were odorless. However, the men’s physiological states, and to some extent their thoughts, changed depending on whether the liquid was tears or saline.
When presented with emotionally ambiguous pictures of women’s faces, 17 of 24 men in the experiment found the faces to be less sexually attractive after sniffing tears than after sniffing saline. After the men sniffed tears while watching a somewhat sad movie not of their choosing, they reported an overall reduction in sexual arousal.
These subjective changes were small; changes in physiological measurements were larger.
The concentration of testosterone in the men’s saliva (which reflects the amount circulating in the bloodstream) fell 13 percent after they sniffed tears but stayed the same after sniffing saline. Their physiological state, as measured by skin temperature, heart rate and respiration, also fell after exposure to tears. Functional MRI imaging of their brains similarly showed less activity in areas associated with sexual arousal after smelling tears.
Taken together, the results “jointly suggest that women’s emotional tears contain a chemosignal that reduces sexual arousal in men,” the researchers concluded. “We have . . . identified an emotionally relevant function for tears.”
In an interview, Sobel said that he doesn’t think chemical signaling is unique to women’s tears. His research used them because they were easier to obtain than men’s.
To conduct the study, the research team posted an ad on the Weizmann Institute campus seeking volunteers who could cry easily. About 60 women and one man responded. They were screened to see how easily they cried and to determine the volume of tears they produced.
“We reached this core group of six women criers who could come back to the lab every other day and cry a full” milliliter, Sobel said.
Each woman chose a movie to elicit crying, watching it in private and collecting tears. By far the most successful tear-inducer was the death scene in “The Champ,” a 1979 film starring Jon Voight about an over-the-hill boxer making a comeback to provide a better future for his son, whom he is raising on his own.
“That scene is a winner,” Sobel said. “Emotion labs all over the world use it to establish sad mood.”
Other reliable tear-jerkers were “Life Is Beautiful,” “Terms of Endearment,” “When a Man Loves a Woman” and an Israeli movie, “Broken Wings.”
The researchers now have two male criers and are recruiting more to study the effects of their tears on women and on other men.