randombio.com | science commentary
Saturday, March 23, 2019

Why do humans cry?

Medical science discovers a cure for the tear-jerker—but how safe is it?

W hy do humans cry? In the movie Terminator 2, the robot asked the teenaged John Connor that question. Instead of an explanation, he received a description of it, which would have been incomprehensible to him.

John could have said that crying resembles vomiting during migraine, head injury, or after eating a toxic food item. Vomiting reduces gastric distress and seems to be followed by endorphin production which acts as a reward to the individual for going through all that nasty unpleasant­ness and mess. Likewise, crying reduces the distress caused by toxic emotions.

In other ways crying resembles animal distress calls. These are vocalizations that occur involuntarily when an animal is in pain, and it's hypothesized that emotional crying could have evolved from distress calls or separation calls.[1] However, although distress calls and crying may have a shared evolutionary origin, they have many differences.

For one thing, emotional crying in adulthood is largely characterized by tear production instead of distress vocalizations.[1] Some ethnobiologists still adhere to the idea that this silent crying is an attempt to gain assistance, but this doesn't explain why movies, music, art or other emotionally charged stimuli can elicit a copious release of water, electrolytes, and proteins from the lacrimal gland accompanied by intense internal feelings.

Moreover, much crying, at least in adults, occurs in private, and humans conceal it because it is interpreted as a form of weakness. In addition, humans have more efficient, and much less painful, ways of communicating distress. This casts doubt on the distress call theory.

Some researchers claim, using arguments from evolutionary biology, that crying strengthens interpersonal relationships by signaling a need for cohesion, but this too is almost certainly a side-effect, because crying can just as easily destroy cohesion. It has even been claimed on the Internet that tears blur one's vision and the reduced visual acuity signals vulnerability.

That's the beauty of the Internet: if the theory shows up there, we know it's wrong. Those rumors that cats come to comfort you when you're crying are also wrong; the cat is probably thinking you're a wounded animal and is tasting you to find out if you are now edible.

There are many kinds of crying

One of the problems is that there are different kinds of crying. The crying that infants and children do is clearly designed to attract attention and sympathy. Then there is screaming, which all humans do involuntarily when in extreme pain. Screaming is a classic distress call that acts as a signal requesting immediate help and strategic advice.

To say that emotional crying, as from sadness, loss, hearing a beloved one's voice, or experiencing beauty, is merely a social behavior intended to elicit comfort would be to confuse the event with its effect on sympathetic bystanders. Most crying indicates genuine suffering and a loss of control; the latter is common in certain neurological disorders. For example, one patient had suicidal ideation, depression, and hopelessness along with unrelenting crying that was caused by a plaque related to multiple sclerosis lateral to her corpus callosum.[2] This is what neurologists call a pseudobulbar affect[3] (‘bulb’ being an old term for the pontine-medullary region of the brain). The crying was not affected by SSRIs but disappeared after treatment with valproic acid, an anti-seizure medication. But just because brain dysfunction can produce crying, it does not mean that crying serves no purpose or that its purpose is communication.

One clue is that a person on the verge of crying experiences a marked increase in emotional sensitivity toward the behavior of others. Thus, one theory is that crying is a desensitizing mechanism for frustrated empathetic behavior.

For example, an adult may feel a great loss and cry when hearing about an unknown child or teenager who has committed suicide (such as that 19 year old Parkland survivor in Florida who recently killed herself out of survival guilt), but have no such response when they discover that the local grocery store is out of short ribs, as personally devastating as that may be. Crying occurs primarily in the context of human interactions as an attachment behaviour, suggesting that empathy pathways in the brain can play a role.

However, it has not yet been established whether oxytocin (the so-called empathy hormone) or endogenous opioids are involved. By contrast, SSRIs (selective serotonin reuptake inhibitors) are potent inhibitors of crying. In one experi­ment, 100 female college students who had consumed alcohol were found to cry more than sober ones after being exposed to emotional movies (Once Were Warriors and Brian's Song)[4], confirming a role for emotional disinhibition. The SSRI antide­pressant paroxetine cured it. Later research showed that testosterone had a similar effect.

And yes, you read that right: modern medicine has found a cure for the tear-jerker!


Even though crying is a social attachment behavior, crying also occurs in isolated and depressed patients who experience hopelessness and despair, conditions that are risk factors for suicide.

According to the interpersonal theory of suicide[5], a person is at risk of suicide when three factors are present: thwarted belongingness, perceived burdensomeness, and the capability of suicide. This theory may oversimplify things[6] and has been criticized as reductionist. In particular, ‘burdensomeness’ may instead be an expression of feelings of worthlessness that accompany depression. There is also the ‘cry of pain’ model[7], which says that suicidal behavior is a response to a stressful situation that has three components: defeat, no escape, and no rescue. This theory says the suicidal person feels trapped with no way out. However, current suicide prediction models have almost zero accuracy in predicting a future event.[8]

People often say that crying leaves them emotionally drained, suggesting that certain classes of emotional feelings or motivations demand to be expressed and that crying may serve as a safety valve for motivated behaviors for which no other means of expression are possible, as for example after the loss or departure of a loved one.

So far, though, we have only theories. Crying is very complex. It must have evolved for some beneficial purpose, but how it works and what that purpose may be is still a great mystery in science. If crying really is a safety valve that allows people to express strong emotions, then using drugs such as SSRIs that block this expression in an attempt to treat depression could have serious unrecognized consequences.

What is not a mystery is that describing it in terms of peptide hormones or as a form of communication is not an adequate explanation. Indeed, reading paper after paper that fails to distinguish crying from pain distress calls and baby vocalizations is enough to bring tears of despair to any biologist.

1. Bylsma LM, Gracanin A, Vingerhoets AJJM (2019). The neurobiology of human crying. Clin Auton Res. 29(1), 63–73. doi: 10.1007/s10286-018-0526-y. Link

2. Johnson B, Nichols S (2015). Crying and suicidal, but not depressed. Pseudobulbar affect in multiple sclerosis successfully treated with valproic acid: Case report and literature review. Palliat Support Care. 13(6), 1797–1801. doi: 10.1017/S1478951514000376. Link

3. Sauvé WM (2016). Recognizing and treating pseudobulbar affect. CNS Spectr. 21(S1), 34–44. doi: 10.1017/S1092852916000791. Link [paywalled]

4. Van der Veen FM, Jorritsma J, Krijger C, Vingerhoets AJJM (2012). Paroxetine reduces crying in young women watching emotional movies. Psychopharmacology (Ber.) 220, 303–308

5. Van Orden KA, Witte TK, Cukrowicz KC, Braithwaite SR, Selby EA, Joiner TE Jr (2010). The interpersonal theory of suicide. Psychol Rev. 117(2), 575–600. doi: 10.1037/a0018697. Link See also the book Why people die by suicide (2005, Harvard Univ. Press) by TE Joiner

6. Hjelmeland H, Loa Knizek B (2019). The emperor's new clothes? A critical look at the interpersonal theory of suicide. Death Stud. Jan 29, 1–11. doi: 10.1080/07481187.2018.1527796. Link

7. Rasmussen SA, Fraser L, Gotz M, MacHale S, Mackie R, Masterton G, McConachie S, O'Connor RC (2010). Elaborating the cry of pain model of suicidality: Testing a psychological model in a sample of first-time and repeat self-harm patients. Br J Clin Psychol. 49(Pt 1), 15–30. doi: 10.1348/014466509X415735. Link

8. Belsher BE, Smolenski DJ, Pruitt LD, Bush NE, Beech EH, Workman DE, Morgan RL, Evatt DP, Tucker J, Skopp NA (2019). Prediction Models for Suicide Attempts and Deaths: A Systematic Review and Simulation. JAMA Psychiatry. Mar 13. doi: 10.1001/jamapsychiatry.2019.0174. Link

march 23 2019, 11:53 am. edited mar 25, 2:42 am

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