It was customary for Ancient Greek mourners to catch their tears in vials and bury them with their loved ones to show the extent of the sorrow for their deaths. Charles Darwin called crying “a special expression of man”, as it is a phenomenon unique to human beings. Scientists, philosophers and psychologists throughout history have speculated extensively on the origins and function of tears, but there is still much that science cannot explain. Are tears a form of vital emotional expression or just the body’s way of turning distress into a bodily function? In order to understand the science of crying we must start at the genesis of tears in the body, the lacrimal glands, commonly known as “tear glands”.


Tears flow through tear ducts in glands located in the upper eyelids. There are three types of tears. All higher animals produce basal tears to regularly lubricate the eyeballs to guard against dust, and protect against infection. The tears we experience when we cut an onion are reflex tears, which are released at the detection of smoke, foreign objects or irritants entering the eye, such as the propenyl sulphuric acid contained in onions. The third type, emotional tears, are a little harder to explain. What is physiologically different about these tears is that they have a distinctive chemical make-up, containing more hormones and protein.

Crying occurs when the tear ducts produce too many tears to be taken back into the nose (where they usually end up) and they brim over and run down our cheeks. We also produce tears when we laugh and yawn, which is due to unnatural facial contortions squeezing our lacrimal glands.

Like many things, we take the ability to cry for granted. Owing to a disorder of the tear glands, people with dry eye usually caused by Sjogren’s syndrome are unable to cry and have to use artificial tears regularly to keep the eyes lubricated. Brain damage to the frontal lobe can cause the opposite problem, pathological crying. It is a disorder of emotional expression in which the part of the brain that regulates the execution of emotional tears in response to a situational stimulus is damaged. The patient is no longer able to associate their feelings of happiness or sadness with the act of crying and will weep uncontrollably for hours at a time. In a bizarre case of crying disorder, a patient researchers call “Eloise”, developed a rare condition called alternating unilateral lachrymation. Each eye would produce tears separately. Reportedly, Eloise cried from one eye when she thought about her mother, and from the other when she thought about her father. If she was prompted to cry whilst thinking about anything other than her parents, she would produce tears from both eyes.


In 18th century Europe men were revered for their sensitivity and would cry openly in public places, especially at the opera. Two centuries later a study by biochemist William Frey reveals unsurprisingly that women cry four times more often than men and for generally longer periods. Results of a survey by psychologist De Fruyt found that women see crying more as a coping mechanism than men do. Women are more likely to cry for both negative and positive reasons while men are more prone to weeping over negative reasons only. According to evolutionary biologists, these differences between the genders in expressions of grief may have an evolutionary basis. This theory is also supported by physiology; men and women’s tear glands are actually structurally different. Boys and girls actually cry equal amounts, but this changes significantly after puberty. Females develop substantial amounts of the hormone prolactin (which controls fluid balance in the body), which is thought to cause weepiness.


In Leonardo Da Vinci’s drawings of the inner workings of the body he sketched a link between the heart and the tear ducts in the eyes. We cry emotional tears when we feel depressed, angry, happy, frustrated, sentimental and stressed. The reasons underlying this behaviour are uncertain and contentious.

There may be an evolutionary basis for why we cry. Salt-water crocodiles and seals produce tears in order to remove salt from their bodies. Scientist Elaine Morgan believes that the act of crying along with other biological oddities such as hairlessness, supports her contention that some time during human evolution we were sea dwellers, and that at that time our tear ducts were used for that purpose. This theory does not offer why however we respond to certain stimuli when we cry, as animal crying is purely physiological.

Frey believes that the origins of crying are in the hormones. He studied the brains of chronic depressive patients and discovered a build up of manganese, a substance that can also be found in emotional tears. Crying may be therefore just the body’s way of removing stress-causing substances from the body.

Physiologist Darlene Dartt builds on Frey’s findings. Her studies reveal that the nervous system may be responsible for crying. Neurotransmitters send out chemical messages to be received by the tear glands. Working in conjunction with pituitary hormones, Dartt believes that nerves provide the “biological pathway to emotional tears”.

Others have put forward that tears may be a by-product of increased autonomic activity of the brain in stressed individuals. The feeling of relief that 85% of females and 73% of males experience after crying supports this contention. Although these theories explain the physiology of crying, they do little to explain the psychology.

Evolutionary biologist Professor Paul Verrel speculates that the rationale behind crying can be traced back to our infancy. Babies cry for reasons like hunger or pain and later learn to cry for attention. Verrell believes that the principal use of crying when we are infants is for communication, and this can be applied to our adult life. Crying is a universal language. We still cry when we request help, or when we offer help and understanding to someone else.

Why crying then, why not another bodily function like yawning or burping? Through the evolutionary process of ritualisation, an association emerged between the process of weeping and communication. Tears have been naturally associated with the eye watering caused by pain and ocular trauma. Perhaps we cry when we are adults when we do not have the words to express our distress, just like when we were infants. This explanation seems to come close to a resolution, but is fallible. Monkey infants are able to alert the attention of their parents by screaming, without the need to actually shed tears. Also, if tears are purely for communication, what then is behind the practice of crying when we are alone?


The ancient philosopher Aristotle believed that weeping is a way of cleaning yourself out emotionally. Is one “use” of crying the catharsis of emotions? Freud discredited this assumption, seeing children’s tears as manipulative and adult tears simply regressive. Descartes believed that emotions are purely reactions of the body and completely apart from the workings of the mind. Are we able to stop crying and show our emotions in a different way? Humanist, scientist and self-pronounced tear expert Tom Lutz believes that ceasing to cry is only a matter of learning to feel something else. Through conditioning, the Tiv people of northern Nigeria find other forms of communication than tears. Parents discourage infants from crying by punishing them at the first sight of a tear. On the other hand, some cultures like the Colombian Kogi adults are particularly emotional, as they allow their babies to cry freely for long stretches of time. There is further scientific reason not to link catharsis with crying. People with a tendency towards depression did not cry more often than a control group in a study by Frey.

What science and psychology have yet to explain is why we cry at a moment of pure happiness or profundity. Why do we cry when we watch a sunset or engage with a beautiful work of art? Medieval monks considered these so-called “tears of enlightenment” to be sacred. Tears have intrigued and mystified the great minds all throughout history. Still, crying remains one of those mysteries unquantifiable by scientific or psychological study. It is impossible, for instance, to find a reason why - like every snowflake and fingerprint - the makeup of every teardrop is utterly unique.

From A Crying Shame: The Science of Tears by Heather Corkhill (me!) 2001.