Tearful Serenity: Crying Away the Stress

Biology 103
2003 Third Paper
On Serendip

Tearful Serenity: Crying Away the Stress

Nomi Kaim

Some days you've just had it. You've been talked at all day by people you couldn't care less about, the lady at the convenience store snapped at you, your friend invited herself over right when you had exactly one hour to write a paper, you got caught in a traffic jam going shopping, you're starting to seriously rethink your life career ... and now there's a thirty dollar parking ticket stuck on your windshield because that darn machine wasn't accepting quarters.

You burst into tears.

Tears, stupid tears! Always coming when you least want them. Now everyone on the street is looking at you and your eyes are so blurry you trip over the bumper and stumble into the street. What a klutz. How humiliating! Why do you always have to cry like this?

But everybody cries. For its capacity to signal physical or emotional distress, crying has left an indelible mark on the slate of human history. Where would art and poetry be without tears? In fact, where would we be? In truth, crying plays an essential role in our biology as well as our social and cultural experiences. We can't stop the tears from flowing, but we can investigate why they flow – and why crying might not be, after all, such a bad thing to do.

Tears are body excretions, just like sweat and mucous and urine. We don't usually like to think about body excretions, but when we do, we bear with them because we know they have important functions. Sweat removes excess salts from the body and cools us; mucous traps surrounding pathogens; urine and feces expel unneeded, toxic waste products that would harm the body if they remained within it. All three contribute to the body's self-regulatory or homeostatic nature, readjusting for balance. Tears, too, must serve a biological, homeostatic purpose. But what? In fact, there are three known answers to this question.

Scientists distinguish three kinds of tears, which differ from each other by function and also, probably, by composition. Basal tears actually form continuously. We don't experience these minute secretions as tears because they don't "ball up" as we are used to tears doing; instead, every time we blink, our eyelids spread the basal solution out over the surface of our eyeballs(1). Basal tears keep our eyes lubricated, important in preventing damage by air currents and bits of floating debris(2), (3).

Basal tears, like all tears, have numerous components. A little bit of mucus allows them to adhere to the eye surface without causing harm. The main part of a tear contains, predictably, water and salts (like sodium chloride and potassium chloride). The ratio of salt to water in tears is typically similar to that of the rest of the body, so there is no net change in salt concentration; nonetheless, if the body's salt concentration climbs too high, it will take advantage of the tear solution and instill it with extra salt. Tears also have antibodies that defend against pathogenic microbes, and enzymes which also contribute to destroying any bacteria the eye encounters(1), (4). A thin layer of oil covers the tear's outside to discourage it from falling out of the eye before its work has been done(5).

Our eyes produce irritant tears when hit by wind or sand (or insects or rocks). Irritant, or reflex, tears have the same constituents as basal tears, and work toward the same goal: protecting the eyes(1), (6). However, since they are designed to break down and eliminate eyeball-intruders like airborne dust, these tears tend to flow in greater amounts and probably contain a greater concentration of antibodies and enzymes that target micro-organisms. Thus, irritant tears are not just basal tears in greater quantity; different biological processes precede the excretion of the two types of solution.

The voluminous tears that so rapidly move us to frustration or pity are, of course, emotional tears(7). Secreted in moments of intense feeling – sometimes joy, but more often sorrow – these tears aren't there to cleanse the eyes of irritating microbes or debris. Yet they do serve a purpose; the function of emotional tears can be inferred from their constituents. Emotional tears contain much more (maybe 25% more) than basal or irritant tears of a certain important ingredient: proteins(8).

What do proteins do? Well, what can't they do? We know very well they can be involved in anything and everything. The proteins found in emotional tears are hormones that build up to very high levels when the body withstands emotional stress(9).

If the chemicals associated with stress did not discharge at all, they would build up to toxic levels that could weaken the body's immune system and other biological processes. But here, as in other areas, the body has its own mechanisms of coping. We secrete stress chemicals when we sweat and when we cry. Clearly, then, it is physically very healthy to cry, regardless of whether or not it feels awkward or embarrassing socially. The reason people will frequently report feeling better after a well-placed cry is doubtless connected to the discharge of stress-related proteins(10); some of the proteins excreted in tears are even associated with the experience of physical pain, rendering weeping a physiologically pain-reducing process(8). Conversely, the state of clinical depression – in which many of the body's self-healing processes appear to "shut down," including, often, emotional tears – is most likely exacerbated by the tearless victim's inability to adequately discharge her pent-up stress. Psychologists refer to freely weeping as an important stage in the healing process. But although this notion may appear to be psychological in origin, involving the confrontation of one's own grief, it also just applies physiologically: crying can reduce levels of stress hormones. Rejuvenating!

One major stress hormone released from the body via tears, prolactin, is found in much higher concentration in women's bodies than in men's. (This makes sense when you consider that the hormone is also implicated in the synthesis of breast milk.) (7), (10) Interestingly, prolactin appears to not only be secreted in tears but also to play a role in the formation of tears. Levels of prolactin in the body correlate positively with frequency of emotional crying(5); as a whole, women cry more often than men (perhaps four times as often, according to one study) and also have a whole lot more prolactin (60% more) (8).

From an evolutionary perspective, why does it make sense for women to cry more often than men? Clearly, this phenomenon plays no minor role in our social interactions; culturally, greater female weepiness is taken for granted in perhaps every area of the world. But why should it be so biologically? Don't men get as stressed out as often as women? Don't they need to release their tension just as much? Perhaps prolactin plays a double role in terms of increasing a person's vulnerability to feeling stress as well as her tendency to cry to discharge that stress. If this is the case, men may not be inclined to get as stressed out as women, who harbor more of the "stress-sensitive" protein prolactin. Thus, women's increased reliance on tears for stress-release may be their bodies' way of maintaining homeostasis. They take in more stress, they pour out more. The fact that men's tear glands are, as a whole, structurally smaller than women's supports the notion that they are used less(10).

But this theory seems faulty. I have seen many men become just as overwhelmed as women by the fast-paced, demanding culture we live in. Prolactin is not the only stress hormone, after all. In all likelihood, men have higher concentrations of other stress-related hormones than women. It could be, instead, that men discharge of their stress by different channels. Men tend to sweat more than women, and sweat contains many of the same chemicals as tears. Perhaps their sweating reduces men's stress in a fashion comparable to women's crying. Men might also urinate more, another way to rid the body of built-up waste products. In fact, it makes sense evolutionarily that men would benefit from discharging stress chemicals in ways other than crying; heavy crying blurs the eyes and prevents vision, antithetical to tears' most basic eye-preserving function. Men, traditionally the hunters, would need to be able to see their prey to survive. But hunting has got to be stressful! Either the age-old trials and tribulations of hunting molded men into organisms less vulnerable to stress (which would support the original hypothesis involving prolactin as the stress-hormone), or men have been releasing their stress through alternate pathways. Sweat, which does not usually impede vision, would be a functional alternative. (Men's evolutionary tendency for increased excretion efficiency over women is evidenced by the way they urinate. In the heat of the jungle, pursuing a wooly mammoth, it pays not to have to sit down to pee.)

If blurry eyes were a nuisance to prehistoric men, they could not have been a great boon for women, either. With their annoying propensity to cut off vision, how did emotional tears survive the test of time? None of the body's other natural processes involve the suppression of one of its basic senses. We need our eyes to see!

Perhaps, once again, our bodies take care of this problem implicitly. Tears, along with saliva, stomach acids and other secretions, are generally only produced when the body is in a state of quiescence or calm. These functions are under the control of the parasympathetic nervous system, a system that operates most efficiently when there's nothing too exciting going on to stimulate the body(11). After all, it would be unreasonable for your body to focus its energy on digesting your breakfast when you're being pursued by, say, a saber-toothed tiger! Same goes for emotional tears – and, indeed, for the feelings associated with them. We don't fully realize our fear and sadness until after the fact, when we get the chance to sit down, cry, and de-stress. Maybe, in the course of our evolution, our ancestors could afford to lose their vision to tears sometimes so long as they limited their crying to after the trauma. Nonetheless, it seems odd to me that a process which so blatantly interferes with one of the senses should survive until today. It's a good reminder that evolution is a work in progress!

One of the reasons emotional tears so fascinate people is that we don't see them in other species. All animals go to the bathroom; many animals sweat. All animals lubricate their eyes with basal tears. However, discounting a few unverified tales of weepy gorillas and elephants (which may well prove, someday, to be accurate), it seems humans are the only ones to cry(10). Why?

Emotional tears may be a piece of the equation that renders human beings biologically and culturally unique (or so we think...). We know our enlarged cerebrums and manual dexterity afford us thoughts and social liaisons as yet unwitnessed in other species. Our faces also hold the key to wonderful communication; we can smile, and we can cry. Smiling clearly developed chiefly for social purposes; crying, on the other hand, may have begun as a solely biological mechanism (for reducing stress) and then acquired an important social meaning. And so crying evolved for the dual purpose of physically dissipating tension and conveying profound emotion.

It may seem, when you cry in public, as though your body has failed you; a mistake, you think; should have been saved for later; sort of like peeing in your pants. It is more likely, however, that you have reached a level of stress that is detrimental to your health. You should let it out. It's okay to cry.

It is good to cry.

End Note:

Though emotional tears are likely unique to humans, all animals secrete irritant tears, and some secrete them in greater volumes than human beings. It is interesting to note that sea animals, including birds, rely most heavily on tears for removing salts from their bodies(10). Do these animals harbor especially high levels of salts because they originated in the ocean? But so did humans. Is it because they eat salty sea-foods? Or perhaps the vicious ocean winds cause increased irritant tearing in these animals, so they evolved to make good biological use of their bountiful tears?

References

1)Tears: Why Do We Cry?, readable school website describing the physiology of tears

2)Crocodilian Biology Database: Do crocodiles cry 'crocodile tears'?, some fun facts about crocodiles and crying

3)Science and the Creator: "My tears into Thy bottle", an interesting religious take on the enigma of human tears

4)Re: What are tears made from?, a little e-mailed message summarizing the composition and functions of basal tears – very brief

5)Tears, good source of information on the role of tears and crying patterns in men and women

6)Do Animals Shed Emotional Tears?, information and speculation on animals and tears

7)Why do we cry?, a few concise facts about tear composition and crying patterns

8) There is Healing in Your Tears, a personal tear story, some tear facts, and a bit of common-sense advice on crying

9)Tears, highly readable information and history of tear research, set in the context of child abuse

10)Sob story: why we cry, and how, interesting Boston Globe article covering a lot of details on tear composition and function

11)Sympathetic Innervation, complex information on the sympathetic and parasympathetic nervous systems

Comments made prior to 2007

I just wanted to say how interesting and insightful I found Nomi Kaim's paper 'Tearful Serenity: Crying Away The Stress'. Earlier today, I found myself wondering, randomly, about the biological reasons we cry, and after doing a google search on the subject, this article was what I found.

Although I no longer do Biology, and some of the more detailed scientific elements within the paper were a little hard to grasp, it was still a wholesome and interesting read, and helped me to reconsider the possible answers to the question I had asked myself earlier in the day.

I would like to congratulate the author of the piece on their work; I hope they achieved a high grade for their efforts! I would also like to thank you for posting such interesting examples of students' work on this website ... Alison Finlay, 4 September 2006

At the end of your article, you brought up evolution. Just thought I'd inform you that humans were created by God, not evolved from the ocean. God created humans. And what might help you is that evolution definitley has not been scientifically proven. If anything, science supports creationism ... Saphira, 19 April 2007