In ophthalmology, a distinction is made between three kinds of tears:

1. Basal tears are important for protection and fueling of the eye, and they facilitate vision. They are released with every eye blink by small tear glands under the eyelid.
2. Irritant or reflex tears are produced in reaction to things like onions, tear gas, infections, and wind, to wash away irritants. They are released by the large lacrimal glands, which are located in the upper, outer portion of each eye orbit.
3. Emotional tears are also released from the lacrimal glands. They are produced when we experience strong emotions—in particular, powerlessness or helplessness or when we have lost significant others.

The lacrimal puncta, located at the inner corner of the eyelids, pass the tears through the lacrimal canaliculi on to the lacrimal sac, which passes them to the nasolacrimal duct, which dumps them out into the nose. When the capacity of the lacrimal puncta to drain the tears is not sufficient, they overflow and start rolling over our cheeks.

Although there are several anecdotes of weeping horses, crocodiles, deer, cows, elephants, and gorillas, there is really no adequately documented case. So, we assume that crying is a uniquely human behavior. At best, it is extremely exceptional in other animals (apes, elephants, camels?). However, animals may have their own specific care-eliciting behaviors, which have very similar functions as baby crying.

Scientists agree that human crying originates from so-called “separation calls,” which can be observed in all mammals and many birds. When infants are removed from their parents, for example, they start making noises, but without tears.

When animals grow older, most species no longer emit these distress signals. In humans, however, there is a shift from the acoustic signal, emitted in all directions, toward the visual signal of tears, which especially fit closer, more intimate interactions.

There are two major differences in crying between humans and other animals:

1. Only humans produce emotional tears.
2. Humans still cry in their adult life (which is very exceptional in the animal kingdom).

My own speculation is that the reason has to do with the fact that our neocortex developed considerably, mainly the part responsible for the processing of visual information (at the cost of olfactory information). Since with two exceptions (tears and blushing) our facial muscles suffice to express emotions, I also assume that crying is very important as a signal, which has contributed to the tears.

Tears are extremely important for transmitting a message of helplessness and need of succor, as well as for the reduction of aggression in potential assaulters. For women with young children, who might cry more easily, it might be a very important behavior to protect themselves and their children against aggression.

A very interesting hypothesis is that tears have also contributed to the development of social coherence in humans. We collaborate intensively, we care for the disabled and the sick, and we can be altruistic and empathic. There is now ample evidence that the sight of tears has a major impact on how we perceive the crying individual and how we tend to react to that person. Note that visible tears were probably among the first signals (e.g., in the case of eye infection) that displayed a strong need for help and care.

Humans are also unique in that they have an especially prolonged childhood—a period in which their motor skills are well developed, but they nevertheless are still greatly dependent on adults. When we are babies, acoustical crying is a very effective way to attract the attention of others (parents, caregivers, but also neutral strangers and potential aggressors or assaulters). Thus, while being a very important behavior (“an acoustical umbilical cord”), it is at the same time a dangerous behavior that can jeopardize the infant. It could be argued that it makes perfect sense to replace the acoustic crying by a visual variant, as soon as the infant has developed the motor skills to move toward or away from others. In that sense, weeping can be considered as a “light” variant of (acoustical) crying.

As humans get older, they cry less frequently and for changing reasons. I think the development of tears over the lifespan is as follows: We first shed basal tears, which are important for protecting our eyes and facilitating vision (these are produced by tear glands that are already available in fetuses). Then come the following tears, all secreted from the lacrimal gland: physical pain tears (in response to things like onions, infection, and wind), emotional pain tears, empathic pain tears, societal pain tears, and sentimental tears (like tears shed in “positive” situations). Interestingly, the positive reasons we cry are nearly always the opposite of the well-known negative triggers that evoke crying (e.g., death–birth, separation–reunion, defeat–victory, conflict–harmony).

Rather than sadness, investigators agree that the key antecedents to crying are helplessness, hopelessness, and the lack of adequate behavioral responses to a problem situation. In addition, there is the loss or separation from loved ones. Deaths, divorces, and homesickness are among the most important triggers of crying.

While these triggers stay important over the lifespan, other triggers change remarkably. For example, whereas physical pain and hurt is important for children and even adolescents, for adults and the elderly they are less relevant. On the other hand, when we grow older, we come to cry more often for the suffering of others (empathy, compassion) and for “positive” reasons.

Humans are most likely to cry to get help and comfort, and possibly sometimes to reduce aggression.

Some investigators emphasize that crying mainly serves intra-personal functions. They feel that crying is beneficial for the crying individual because it helps to make the person feel better; in other words, it facilitates emotional recovery. This is also known as the putative cathartic function of crying. Alternatively, there are those who think that the main function of crying can be found in its inter-personal effects. Crying and tears are a powerful signal to others that you are in need.

It must be stressed that there is evidence that the postulated cathartic effects of crying may also result from the positive and comforting reactions of others, rather than from the act of crying per se.

Some people doubt whether we ever cry for positive reasons. Very often, it is possible to explain this type of crying with the idea that in especially happy moments, we allow ourselves to reflect on less joyful moments. For example, during a reunion, we may actually cry for all the time that we have missed each other. When Dutch horsewoman Anky van Grunsven received her Olympic gold medal, she explained that she actually cried because her father had died a few months earlier. She was sad that he could not experience this highlight. And when we get married, it is also the end of a certain phase in life, and it may involve a more definite separation from our parents. These are elements that may evoke negative feelings.

Very positive emotions may also evoke a kind of helplessness: We simply do not know how to express our extreme joy. This inability to adequately express how we feel might result in tears.

The following factors are associated with individual differences and group differences:

• Gender
• Temperament (personality)
• Attachment style
• Socialization
• Feelings of lonesomeness or romantic status
• Transition to parenthood
• Psychological state (depression, homesickness)
• Stressful or traumatic life events
• Drug use (alcohol, cocaine)
• Physical state (fatigue, hormones)
• Neurological disorders

What is further important is that the differences may result from very different causes, or any combination of these factors:

• A difference in the amount of exposure to emotional stimuli (for example, females are more likely to watch tearjerkers than men are!)
• A difference in how (emotional) stimuli are appraised
• A difference in the crying threshold (due to things like sleep loss or hormonal influences)
• A difference in the capacity to control their tears

The difference in crying between men and women can be the result of one, or a combination, of several factors that often work together.

First, we should not overlook that men and women differ in their exposure to emotion-inducing situations. Women seem to have higher empathic skills, their bonds with other women are different in nature than male bonds, they are more likely to work in health care or with children, they watch more sad movies and read more about broken marriages and unhappy children, and they are more likely to be depressed or suffer from pain syndromes. In addition, women seem more likely to react with helplessness, which may induce tears (e.g., in conflicts they experience a powerless anger). Then, there are the sex hormones. The male sex hormone testosterone seems to inhibit crying, while the female hormone prolactin may lower the threshold. Finally, males (especially boys) suffer from more environmental pressure (in particular from their peers) to control their tears.

Culture may have an effect on the specific reasons that people cry, on how and how often they cry, the effects of crying, and how crying individuals are perceived. It also may influence how parents deal with the crying of babies and children, as well as on the degree of the gender difference in crying.

At the country level, differences in freedom of expression and personality—rather than suffering or distress—tend to contribute to how much people cry. People living in cold (northern) countries cry more often than people in warmer countries, and those living in wealthier, more democratic, and more individualistic countries report crying more often. Surprisingly, gender difference in crying is also considerably larger in countries where there is more equality between men and women than in societies in which there are still large societal differences between males and females.

But it is important to make a distinction between crying in the intimate setting—in a person’s own house, hut, or igloo, with no strangers present—and crying in a public setting, with many others present, in which so-called display rules and factors as shame play a major role. I strongly feel that there are not too many cultural differences in crying in intimate settings (which account for 70 to 80 percent of all crying episodes), but crying in public settings may heavily depend on cultural influences. For example, there are Indian tribes in which people cry as a greeting ritual, and crying can also be observed in some cultures during all kinds of celebrations, ceremonies, rituals, or prayer.

First of all, I must emphasize that I am not a clinical psychologist, so I do not have any experience with treating patients, and I also have never done an evaluation of the effectiveness of treatments for this purpose. So, my knowledge is modest.

I only can say that in theory, there are two options. A psychological treatment that has been described in the psychological literature and a pharmaceutical solution. SSRIs reportedly have, even in a rather low concentration and rather immediately (after an hour or so), an inhibiting effect on crying. These have also been applied in patients with a stroke or other brain disorders, who suffer from "pathological" crying.

In addition, case studies have been reported in which desensitization (Field, 1970) and contingency management (Redd, 1982) have resulted in decreases in crying. Two studies have used anger, either assertiveness training for anger expression (Rimm, 1967) or imagery of others getting angry (Tasto & Chesney, 1977) to decrease crying frequency in individuals.

Sometime people suffer from uncontrollable and excessive crying as a consequence of brain disorders (stroke, MS, certain form of epilepsy, dementia, etc.). In the literature this is labeled as “Pseudobulbar Affect”, “emotional lability,” “reflex crying,” “pathological crying,” or “labile mood”. Characteristic are:

• Rapid mood changes — a person may “spill over into tears” for no obvious reason and then quickly stop crying or start laughing.
• Crying or laughing that doesn’t match a person’s mood.
• Crying or laughing at unusual times or that lasts longer than seems appropriate.

This excessive crying can be treated with psychopharmacological agents (see: Hacket et al., 2010; Wortzel, 2008). These psychopharmacological treatments may also be considered for excessive crying of a different origin.

• Field, P.B. (1970). Preventing crying through desensitization. American Journal of Clinical Hypnosis, 13, 134-136.
• Hackett, M.L., Yang, M., Anderson, C.S., Horrocks, J.A., & House, A. (2010). Pharmaceutical interventions for emotionalism after stroke. Stroke, 41, 460-461.
• Redd, W.H. (1982). Treatment of excessive crying in a terminal cancer patient. Journal of Behavioral Medicine, 5, 225-235.
• Rimm, D.C. (1967). Assertive training used in a treatment of chronic crying spells. Behavior Research and Therapy, 5, 373-374.
• Tasto, D.L., & Chesney, M.A. (1977). The deconditioning of nausea and of crying by emotive imagery. Journal of Behavior Therapy and Experimental Psychiatry, 8, 139-142.
• Wortzel, H.S., Oster, T.J., Anderson, C.A., & Arciniegas, D.B. (2008). Pathological laughing and crying: Epidemiology, pathophysiology and treatment. CNS Drugs, 22, 531-545.

We believe that tears, in a much similar way as our big toes were essential because they allowed us to stand an walk in an upright position, and our thumbs, because they allowed us to manipulate objects and to design and use instruments, were important for the development of our empathic skills and, relatedly, our moral and prosocial development. Our most recent findings confirm that (genuinely) crying individuals are perceived as more honest and reliable than non-crying and certainly as fake crying people.

In my view, crying is a biopsychosocial phenomenon, which means that any of these three factors can play a crucial role, but these influences are changing, dependent on the specific person and situation. Our crying threshold is partly generically determined, but can also fluctuate due to factors like sleep deprivation, use of alcohol or drugs, romantic status, parental status, having experienced strong emotional experiences or traumas, but also hormonal levels and specific brain damage.

Sometimes, journalists ask me which results I regard as the most surprising. First, I was surprised when we found that only 50% of the respondents reported improved mood after their crying episode. Also, the fact that people with mental health problems, although maybe crying more often, seldom if ever reported beneficial effects of crying was not expected. That also holds for the fact that how people feel after crying is predominantly determined by how observers respond to their crying.

A second surprising finding was that there is such a remarkable diurnal rhythm of adult crying over the day. From 04.00 AM until 11.00 PM it is more like that adults cry. And they do that preferably at home, alone or in the presence of their mother or romantic partner.

Still another amazing finding, even entirely contrary to expectations, was that most crying seems to occur not in the southern cultures that are well-known for their emotional expressivity, but rather in colder, northern (e.g., Scandinavian) countries.

Still another unexpected finding was that we perceive crying people, not particularly as weak and not competent, but especially as warm, reliable, and honest.

A bit related to the last finding, I was surprised in the interest of forensic psychologists in our work, because they felt that our research methods might be helpful to develop a more objective way to assess empathy. That would be a very nice example of unanticipated spin-off of a fundamental research project.