The fact that we cry when we're feeling sad, overjoyed, or otherwise emotional is thought to be a uniquely human trait. But biologists long suspected tears have some other function, and now we might know: they reduce men's sexual arousal.
We know that there are actual chemical differences between the tears that we cry when we're emotional and the saline tears our eyes produce strictly to protect themselves from debris. In other species like mice, tears are known to have chemical signals that send "messages" to other mice that smell them. Researchers at Israel's Weizmann Institute of Science decided to find out whether our tears send their own chemical messages, and the results were pretty extraordinary.
The researchers collected tears from women who were watching a sad movie, and then they gathered up saline tears from the same women. Then, in a double blind experiment - meaning neither the male test subjects nor the researchers knew which tears were which - the researchers asked the test subjects to smell the tears. Regardless of whether they were given the tears or the saline, the men said the water had no discernible odor.
But a lack of odor doesn't mean the tears didn't affect them. The men were then shown photographs of women, and those who had sniffed the tears consistently found the women less sexually attractive than did the men who had smelled the saline water. The ones who smelled tears also showed decreased signs of physiological reaction and salivary testosterone.
And that isn't the end of the story. The men were then placed in an MRI machine and watched a sad movie. For the men who had smelled tears, the imaging revealed significantly less activity in the part of their brains that's believed to be responsible for sexual arousal compared to the brains of their saline-sniffing peers.
Now, this was a relatively small study, and these findings will need to be replicated several times before we have a clear handle on how strong this effect really is. We don't know what effect male tears might have on women since that wasn't within the purview of the study, but the researchers suspect male tears have similar effects.