When a woman cries, chemicals in her tears send off signals which reduce sexual arousal in males – their libido goes down, scientists from the Weizmann Institute, Israel, revealed in the journal Science. How and why this happens is still a bit of a mystery because tears have no smell, but they contain compounds which trigger reactions in humans.

Human beings, like other animals, release several compounds in their body fluids that emit subtle messages to other humans. Recent studies have found that human sweat is full of chemicals that carry a wide range of emotional and other signals picked up by those who smell them. In the case of tears, which are odorless, the messages are being picked up in some other way.

In one experiment, Shani Gelstein, Yaara Yeshurun and team collected emotional tears from female participants who were sitting in a secluded room and cried from watching sad movies. They then set out to find out whether males could tell these tears from a saline solution – they were not able to.

In another experiment, men were asked to sniff either a saline solution (control solution) or tears. The tears or saline solution were then applied under their nostrils on a pad while they looked at and commented on various pictures of females on a monitor.

This double-blind test was repeated the following day, but the other way round – those exposed to tears were exposed to the saline solution, and vice-versa.

The scientists found that neither the tears nor the control solution had any impact on the men’s estimates of empathy or sadness expressed in the female’s faces. However, those who had been exposed to tears were negatively impacted when asked to attribute sex appeal to the female faces they were commenting on.

The males were then asked to watch emotional movies while exposed to either tears or the saline solution. They were asked to report on their own mood during the films. Their skin temperatures and heart rates, signs of sexual arousal, were also measured throughout the movie. The researchers analyzed the men’s comments and found that exposure to tears did not have any effect on the males’ empathy, however, their sexual arousal went down slightly.

They also found that the physiological signs of arousal, skin temperature and heart rate, were subdued by exposure to tears. Those exposed to tears also experienced a considerable drop in testosterone levels. Testosterone is a hormone closely linked to sexual arousal.

In another experiment the males did the same, but an fMRI machine which measures brain activity was used. The scans clearly showed lower activity in parts of the brain associated with sexual arousal when the males were exposed to tears.

Sobel said:

“This study raises many interesting questions. What is the chemical involved? Do different kinds of emotional situations send different tear-encoded signals? Are women’s tears different from, say, men’s tears? Children’s tears? This study reinforces the idea that human chemical signals – even ones we’re not conscious of – affect the behavior of others.”

The authors explain that the function of human crying and tears baffled Charles Darwin. Darwin was able to explain several functions of emotional displays, such as the tightening of the mouth in disgust, which he believed comes from a response to spoiled food. The researchers suggest that perhaps their findings may offer an answer to this mystery, that tears have a chemosignal function. Some rodent tears contain similar chemical signals, Sobel pointed out.

Sobel said:

“The uniquely human behavior of emotional tearing may not be so uniquely human after all.”

“Human Tears Contain a Chemosignal”
Shani Gelstein, Yaara Yeshurun, Liron Rozenkrantz, Sagit Shushan, Idan Frumin, Yehudah Roth and Noam Sobel
Science DOI: 10.1126/science.1198331

Written by Christian Nordqvist