A team of Israeli researchers believes that tears send a sexual message that can be summarized as: "Now's not a good time."
In a study published Friday by the journal Science, the researchers report that men who sniff tears cried by sad women experience a temporary decline in both sexual arousal and circulating testosterone, a hormone tied to libido.
"We've identified that there is a chemo-signal in human tears," said Noam Sobel, the researcher at the Weizmann Institute of Science who headed the study.
Only women's tears have been studied so far, but the researchers suspect that men's tears, and possibly children's, also contain chemical signals. They are eager to find out what messages those tears 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 the secretions of anogenital glands. Those fluids contain behavior-altering compounds, known as pheromones. Emotional tears have a different chemical composition from tears shed when the eye is irritated. But the identity of the ardor-quenching substance they contain isn't known.
Sobel and his colleagues collected tears from women who cried after watching a sad scene in a movie. The researchers beforehand trickled saline solution down the cheeks of the women and collected it as a "control" substance.
A group of men were then exposed to the two liquids by sniffing them in vials and, for some of the experiments, by having a small pad soaked with the liquid taped between the nostrils and the 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.
For example, 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 watching a sad movie and sniffing tears during it they also reported an overall reduction in sexual arousal.
These subjective changes were small. Slightly larger were changes in physiological measurements.
Testosterone concentration in saliva, which reflects the amount circulating in the bloodstream, fell 13 percent after sniffing tears but stayed the same after sniffing saline.
Physiological state, as measured by skin temperature, heart rate and respiration, also fell after exposure to tears. Functional MRI imaging of the brain also 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 chemo-signal that reduces sexual arousal in men," the researchers concluded. "We have identified an emotionally relevant function for tears."
In an interview Sobel hastened to add that he doesn't think chemical signaling is unique to women's tears. His research used them simply because they were easier to obtain.
The researchers now have two male criers and are slowly recruiting more in order to study the effects of their tears on women and on other men.