Why do we cry?

Imagine you are having an emotional fight with your partner, or your beloved cat just died or you are watching the end of titanic and you know only one of them will survive. When I am in those situations I start crying uncontrollably. My voice cracks, my nose starts running, I sob and sniff, hardly able to get any words out. And of course tears stream down my face. So much so that I can hardly see what is right in front of me. Afterwards, when I stop to think about it I wonder why? Why do humans cry? All those reactions do not seem very adapted to me and I start asking myself what the advantages of such a behavioral mechanism could be. Some may argue that tears serve a protective function. And there is certainly some truth to this statement. After all tears do carry dirt out of our eyes and keep them moist. But when it comes to emotional tears this logic does not seem to fit. After all sadness, anger or frustration are not as easily swept away as a grain of sand might be. But then why do we cry when we are emotional? It seems quite feasible that emotional tears serve as a signal of our current emotional state to the people around us. Tears draw attention to our distress and in some cases they might cause empathetic kindness or defuse a situation that might otherwise have ended in anger. But is that really all? Are tears just a way to communicate how we feel? Before I go on I want to warn you that I will not be able to tell you the reasons behind why we cry today. But maybe I can give you an insight into whether emotional tears really are just a way to help us express our emotions.

A study on tears and sexual arousal

A recent study by Gelstein et al. (2011) suggests that this is not the case. In this study the authors investigated whether human emotional tears, similarly to the function of tears in other animals such as mice, serve as a chemosignal. Meaning that the smell of the tears alone influences the behavior or mental state of the human exposed to them. In particular the authors hypothesized that smelling emotional tears of women would reduce sexual arousal in men. In a rather interesting setup the authors asked donor women to watch sad films and collect the tears they cried while watching. For the control condition the authors used a saline solution that was trickled down the donor women’s cheek (just to make sure that it smelled like women). While the participants, who were all male, noticed no difference between the two solutions the study revealed behavioral differences in three separate experiments. In each experiment the participants went through both conditions and answered several questions on their current mental state and their perception of the stimuli. In the first experiment the authors discovered that men perceived the emotionally ambiguous pictures of women’s faces as less sexually attractive, but not as sadder while being exposed to the smell of the tears as compared to the control condition. In addition there was no differential effect on empathy for the two solutions. To further investigate the effect of tears on emotion the authors conducted a second experiment where the participants watched a sad film after sniffing one of the two solutions. This time the authors also measured physical indicators of emotion including testosterone levels. Once again there was no differential effect on the sadness ratings (this time the participants were asked for their own mood), but sniffing the tears slightly reduced self-ratings of sexual arousal. In accordance with this finding the testosterone levels were also reduced after sniffing the tears. This reduction did not occur for the saline solution. In the third experiment the authors looked at brain activity via fMRI while watching sad, happy and neutral films. The study showed that there was lower activity in the left fusiform gyrus and hypothalamus in the tears condition as compared to the saline condition. These brain regions are implicated in sexual arousal.

But hold back your horses for now

At this point I feel the need to mention that these results by themselves do not allow the conclusion that sexual arousal really is influenced by smelling emotional tears. Especially in regard to the brain activity one should not forget that these regions are not only important for sexual arousal. Nevertheless the behavioral results, the hormone level changes, as well as the fact that there is a difference in brain activity even though there was no perceived conscious difference between the two odors suggest that emotional tears do emit some chemosignal that is relevant for human behavior.

Back to the beginning

While there is still much to find out about emotional tears and their functions, these recent findings lead me to belief that there is at least more to them than just the expression of emotion. But they also leave me with many still unanswered questions. For example: This study only looked at the effect of tears collected from women on men. But how are women themselves influenced? Is there a gender difference in the effect? Another interesting question is whether this effect is only of short duration. Maybe associating the smell of tears with certain people –that cry easily or often- makes them generally less sexually attractive. It could also be possible that tears influence more than just sexual arousal. But the issue I am most curious about brings me back to my original question. Even though we don’t know anything for certain, if we trust the results of this study and just for the sake of the argument assume that emotional tears really do elicit a chemosignal that reduces the sexual attractivity of women and sexual arousal in men, what we discovered would not be a reason for the existence of emotional tears. It would be an effect. But then again, when it comes to evolution effects might be the driving force behind any change. So even though this study does not allow me to answer my initial question of why humans cry when they are sad, knowing more about the effect of tears brings me closer to the right questions that still need answering to get there. For example the effect of tears on sexual arousal may be a mechanism to reduce the likelihood of involuntary sex. Or maybe tears help humans to be in a mental and physical state that is important for emotional bonding. Furthermore I only spoke about emotional tears elicited in sad situations. But sometimes we also cry when we are relieved, angry or even happy. This raises the question of whether those tears would also contain chemosignal with similar or differing effects. Would those chemosignals then have different functions as well? What I do know is that I at least will be more aware of my own tears from now on and the next time I cry I will think about what my tears might do to the people around me.