Why do we cry?

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1:03So I've got a package that you've sent me. Yeah. It sounds like sweets. Okay. What? This is so far from sweets.

1:19It's like 20 different little vials, little things that you collect liquid in. Indeed. I'm guessing this is going to be where I collect my tears. Well, guess. Super. Hello, I'm Caroline Steele and welcome to CrowdScience from the BBC World Service, the show that answers your science questions. I've got about 50 pipettes and about 20 little vials. You're optimistic with this, OK? Each one of these probably holds more tears than I've cried in my life. I think they're 1.5 mils. My producer Eloise has just sent me a tear collection kit and she's set me a challenge. carry the kit around for the next 10 days and catch any tears that happen to roll down my face.

2:06OK, Operation Make Caroline Cry is well and truly underway. I don't think I'm a big crier and now I'm hoping to cry thanks to 16-year-old listener Lizzie who thought of a question one night at the dinner table with her family. Why do we cry? We were just wondering why we cry physically because we sweat to cool down, we shiver to heat up. But why do we physically need to cry? Is it something chemical or is it purely just emotional? And also why girls and women tend to cry more than men and what the evolutionary benefit to crying was. And when you were having this conversation around the dinner table with your family, what did different people say?

2:51My mum was like, it's a build-up of pressure. My dad was like, it could be like your body's way of putting your chemicals and hormones back to a natural state so you can respond to danger better and like have a clearer head and I kind of thought the same thing like it's got to be some sort of like secretion of chemicals but I'm not entirely sure what. So you've noticed that girls or women seem to cry more than men have you got any theories about why that might be? Part of me thinks it's like hormonal so like we have different cycles hormone cycles we're physically different but then obviously there's that social pressure of like men tend to cry less and then that becomes sort of a stereotype so then they've kind of suppressed that but I'm not sure.

3:37Interesting and if you don't mind sharing how much of a crier are you? Oh I cry all the time but but then also So like it definitely depends on other circumstances. Like if I'm extra stressed, then I cry more. If I'm on my period, I cry more. If there's lots of changes around me, I cry more. And when you've let it all out, do you feel better? I think most people will feel better after crying. I always feel like a weight's been lifted off me. Thanks, Lizzie. It sounds like your family has interesting conversations at dinner. Why do we cry? It's a good question. To me, crying feels like a bit of a waste of water, salt and energy.

4:17So it must have some important benefits to justify doing it. Let's start with the basics. Our tears. What are they made of? Tears are made of five components. Mucus, electrolytes, water, proteins and lipids. That's about it. This is Marie Bagné-Elaouet. She's a postdoctoral fellow at the Institute of Human Biology in Switzerland. Marie grew tear glands in Petri dishes for her PhD. So she knows exactly what makes up a tear. The mucus, the water and the lipids make up the tear film and these come out when we cry. The proteins are antiviral and antibacterial and they prevent infections. And the fifth component.

5:01Electrolytes are minerals that are essential for the body functions. So Lizzie was right. We do secrete chemicals in our tears. And it turns out not all tears are built the same. There are different types of tears. They are called the basal tears, the reflex tears and emotional tears. The basal tears are the ones that are always present on the surface of your eye. They keep your eye lubricated. The reflex tears are secreted when an irritant comes into your eye, like a dust or an insect. And then the tear we're probably all quite familiar with. The last type of tear is the emotional tears. those are the ones that are secreted when you feel happy or sad or any other emotion.

5:42There are three different types of tears. And to help answer Lizzie's question, I'm on a mission to get to know them all. First up, basal tears. They're always present, keeping our eye lubricated by forming part of the watery film that covers our eyes. The tear film is made of three different layers. The first layer that touches directly the ocular surface is a mucus layer that contains a lot of sugars. and it helps the tears sticking to the eye. This layer is mostly produced by the conjunctiva. The conjunctiva is what lines the white of the eye and the inside of the eyelids. The second layer of the tirofilm is a water layer.

6:21That layer mostly comes from the tear gland. And the last layer of the tirofilm is a lipid layer that is made by the Maybohmian glands. And this layer prevents the tears from evaporating. In other words, a final oily layer. Nice. Next up, reflex tears. They flush out irritants. To better understand my tears, my plan is to cry them, collect them and then look at them under a microscope. To get things flowing, producer Eloise came over to my house with a gift. OK, Caroline, I'm coming into the kitchen and I present to you an onion. Woohoo! Okay. Ollie, shush, please. It's no secret that chopping onions irritates our eyes.

7:12Come on. I almost feel like I should be chopping with my eyes there. Ooh, they're already getting a little bit juicy. Okay, give me the signal so I know to cut them. I think it's going to be a while. Did I need to get a bigger onion? Oh, here we go. Here's one, here's one, here's one. Oh, no. It turns out that collecting tears isn't simply a case of holding a vial to my cheek and letting a tear roll into it. It's actually a lot more fiddly. Remember those little pipettes? Come on, dear. Oh, there we go. Well, Eloise is holding one to my wet face now and trying to draw a tear into it. Beautiful tears.

7:52Nice.

7:56So what exactly is happening inside my body to produce this tear? Here's biologist Marie again. Your eye knows that it needs to cry because it has a lot of sensory innervation. In particular, the organ is called the cornea. The cornea is a transparent organ that covers the colourful part of your eye. And this is the organ that has the most sensory innervation in your entire body. In other words, our cornea is full of thousands and thousands of neurons or nerve cells. And they're constantly picking up messages. Those neurons are sensory neurons. They can sense a lot of different stimuli. They can sense the temperature.

8:35They can sense mechanical stresses, the dryness of the eye. And just to give you an example, they're already becoming active when the temperature decreases by half a degree. So they're really, really sensitive. Yes, to be fair, I often cry when it's cold. Yeah. This message is then sent to the brain, to a region called the lacrimal nucleus, which in turn sends a message to the tear gland to adjust the amount of tears being produced. Time for our final type of tear, the emotional tear. You know, the kind that spills from your eyes when you feel sad, frustrated, maybe even happy. OK, so I've got some videos that we can watch on my laptop.

9:20Back home, Eloise was about to get up some tear-jerking video clips in the hope that it might start my waterworks. But there was no need. I'd already collected some emotional tears. It's just going to sound like I'm bragging. I ran a marathon. No, no, congratulations. This is a very, very big brag. Not a humble one, a massive one. It was my first one and I had a suspicion that it might make me cry. I actually thought I would cry during it because I was in so much pain. So I carried my pipette and my little vial with me ready to collect any pain tears. But actually, I didn't cry during it. But when I finished it, I just like burst into tears.

10:00So as people were walking past the finish line going to find their friends and family, I was like stationary with a pipette trying to get my tears. Weirdly, I don't know what kind of tears those tears are. Like, I don't really know why I cried. Maybe relief? That was going to be my question. Why do you think you cried? I think relief that it was over and acknowledgement of, oh my gosh, that was really hard. I see, sort of like stress at it being so difficult. Yeah, so either stress at it being so difficult tears or relief tears. I was feeling both of those things. So I guess a mixture of both.

10:34A mysterious cocktail of emotions. But why did it make me cry? When you feel an emotion that is integrated in the brain, and this region of the brain that senses the emotion can communicate with the lacrimal nucleus, which in turn sends a message to the tear gland, to the conjunctiva, and to the meibomian glands to adjust the amount of the tears being produced. So those are the three different types of tears. Basal tears keep our eyes lubricated, reflex tears flush out irritants, and emotional tears pop up when life gets too much. Now I've dutifully collected some reflex and emotional tears, I want to see what they look like under a microscope.

11:23We skipped basil, as I didn't fancy collecting tears from the film of my eye. So I packed my bags, not forgetting my vials, to get on a train to visit a man in the Netherlands who looks at tears in fine detail. And because this train involves international borders, it requires you to go through airport-style security. So I'm at the station. I'm about to get on the train to Rotterdam and I'm about to have to try and smuggle my tears through security. So I'm hoping we don't have to take liquids out our bags, otherwise this could be a little bit awkward. Luckily, I could keep my tears in my bag as I went through security.

11:59Hello. Welcome. So I made it to the Netherlands to meet Maurice Mickers. He's an artist and scientific visualisation researcher. OK, perfect, let's go. Maris is also the founder of the Imaginarium of Tears, which is a collection of photographs of people's tears. A story where I visualise tears of people to tell their unique stories. He does this by putting a single tear on a tiny glass slide, drying it out so it crystallises, looking at it under a microscope and then printing the image on a massive canvas. Turning them into a unique work of art that represents the emotion you felt at that point.

12:38And that story I would like to emphasize and give you the stage to talk about. Yeah, it's sort of a conversation starter into what's probably a difficult story. Yeah, well, let's have a look at mine. Stashed away in this lovely plastic bag. I hand over my vial of onion tears, so reflex tears. So there's a couple of them. Great. Maurice uses a giant pipette to suck them up out of the vial. So what I will do now is I will make these tiny little droplets on the slide. Now we can just wait. For my tears to evaporate. And the waiting is, let's say today, hopefully within 20 minutes. How's the tears looking?

13:24Oh wow, they're looking really white. Yeah, they're going to turn. Initially they look like kind of drops of water, whereas now I'd say they look like, I don't know. Mineral deposits like you would have in the shower. Ah, yes. But what do they look like up close? Maurice puts my onion tear under the microscope. Oh, this is exciting. Adjusts the knobs and... There you go. Ooh. Oh my gosh, that is not at all what I was expecting, not that I really had a clear idea. They kind of look like frozen leaves. Like if you're going on a walk in a park on a really cold day and you've got frosty leaves under your feet.

14:09But yeah, they look really cool.

14:15Right, so let's have a look at my marathon too. I literally have no idea what to expect. Whoa, it looks so different. OK, so this one is some ferns or some leaves from a plant and you left prints of them in some grey kind of background. And then round the very edge, it goes darker. So yeah, it just sort of looks like an amazing patchwork of different leaves, I would say. Yeah, really cool.

14:52It's unclear why my emotional tear looks different from my reflex tear. It might be that different types of tears are made up of different things, but there isn't any concrete research into that just yet. But we do know that factors like temperature, humidity and dust particles in the air can affect the way tears look under a microscope. And Mowry showed me some photos of other people's tears, and they hardly looked related to mine. Oh, whoa! He's got sort of squares in his. She's got kind of like worms on the edge. David looks like shattered glass. Oh, Anna Maria's emotional tear looks like a kind of snowy landscape.

15:31This is so cool. What an amazing project. Yeah, they're all kind of little planets.

15:40All these tears of emotion translated into such varying, complex landscapes. But why do emotions lead to tears in the first place? That's what we'll be finding out next.

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16:58You're listening to CrowdScience from the BBC World Service, the show that pours blood, sweat and tears into answering your science questions. I'm Caroline Steele, and in this episode we're exploring a question from 16-year-old listener Lizzie, who wants to know, why do we cry? I cry when I'm sad, when I'm happy, and for a whole host of other emotions I struggle to put my finger on. But why?

17:28Hi, nice to meet you. Hi. I'm Caroline. Hi. Hi, nice to meet you. I like that you play a bird song in the house. Advinger Hertz is probably the world's leading expert on crying. He's an emeritus professor of psychology at Tilburg University in the Netherlands. And he and his wife invited me and producer Eloise over for breakfast. Oh, wow. What a block of cheese. I think we most often associate tears with feeling sad. So let's start with unhappy tears. Well, that's the first question. Do we really cry when we are sad? Our hypothesis is that we cry, especially when we feel helpless, when we feel a strong need to connect with others.

18:13I certainly cry when I feel helpless, in particular if I've tried really hard to fix something and it just doesn't work. Crying when we feel helpless is a constant throughout our lives. But other reasons to cry change as we get older. For example, physical pain, that's a very important trigger of tears for infants and for children. But for adults and for the elderly, it's far less important. But what you see is that when we grow older, we cry more, not just over our own suffering, but also on the suffering and misery of others. So we develop our empathic skills. As we grow up, we learn to empathise with others.

18:59And what you also see is that it seems as if we start to cry more over positive phenomena. The beauty of art, the beauty of music, the beauty of nature, and even the moral beauty of behaviour of others. So, for example, acts of altruism, self-sacrifice and that kind of behaviour. But in that situation you're not, I guess, helpless? No, maybe to understand it, we can make use of the word overwhelmed. You're overwhelmed by the beauty of a natural scene. You're overwhelmed by the beauty of music. You feel small and void and tiny. Yeah, you've got a sort of sense of awe. Yeah, yeah, yeah, right.

19:54in the tears i was collecting for maurice i ran a marathon not for the experiment um i was running one anyway but i'm not really sure why i cried at the end it's not a clear emotion do you have any idea what might be going on there well what you often see in spot settings Your crying threshold may be low because you're exhausted. Yeah, that's true. That's one thing. But also what often can be is that there is a positive fact. You finish your marathon and at that moment you look back at all the energy that you spent to reach that point. Emotions seldom occur in a pure form. Very often it's a mix or a fast alternation of different emotions.

20:51I can certainly relate to feeling a complicated mix of emotions while I cry. And I tend to feel better afterwards, which is something listener Lizzie has noticed too. But does crying actually provide relief? Lauren Balsmer, a clinical psychologist at the University of Pittsburgh in the US, has been looking into exactly this. We're using heart rate sensors to measure electrocardiogram in relation to when people cry. People might be familiar with that since people often use, you know, things like Fitbit and that sort of thing. Electrocardiograms record the rhythm and rates of our hearts, which can give us some insight into how our nervous system is working.

21:30Our nervous system has two main branches. The sympathetic nervous system, which is responsible for our fight or flight response, and our parasympathetic nervous system, which helps us calm down and relax. It seems that right at the peak of the emotional episode, right before a crying starts, you're at your highest sympathetic arousal, that fight or flight response. And then right after crying starts, that's where we see that increase in this parasympathetic activity, which is basically our rest and digest system. So sort of early data is suggesting that crying might help take us out of the sort of fight or flight response into a more relaxed place.

22:09Right, yeah. So it might be a regulatory function when you're feeling like overwhelmed with emotion, whether positive or negative. Lizzie's dad, you thought that crying could be your body's way of adjusting your hormones to clear your head. And Lauren's research suggests you're onto something. Crying activates our parasympathetic nervous system, which lowers levels of hormones like the stress hormone cortisol. But do these hormones leave our body through our tears? It's like, you know, cry out, cry out the toxins. I've definitely had friends say that to me. I'm pretty sure that's not scientific.

22:44No. As far as Lauren knows, there's only been one study that's looked into this, and it's from the 80s. So William Frey, he had measured tears when people cried to emotional situations versus like if they were cutting an onion. So they were non-emotional tears. So he was trying to compare like stress hormones. And he found that there was more the stress hormones in the emotional tears. But then no one's replicated that in the past 40 years. We don't know from like an ophthalmology perspective that the tears have any sort of function in releasing, you know, bad particles from the body. So Lauren's research shows that crying can help calm us down, which definitely chimes with listener Lizzie's experience.

23:25But that's not always the case. Psychologist Ad's research has found that crying isn't guaranteed to bring relief. It comes down to three factors. First, it was quite a surprise. People who are depressed or who suffer from a burnout, they tend to cry more often, but they hardly, if ever, report that they feel better after a crying episode. So the people who needed it most, they do not benefit. That's very sad. And the second factor was what exactly made us cry. And it appeared also to our surprise that we mainly report improved mood when we cry over controllable situations, but not when we cry over uncontrollable situations.

24:16It doesn't necessarily help when you're grieving, but might help. I don't know if you're worried about a friendship and you have the ability to reach out to the friend and improve it. Yeah, exactly. The third factor that affects whether or not you feel better after having a good cry is the people around you. If they react with understanding and they offer you support and comfort, of course, then you feel better. But if they start ridiculing you or they become angry or you feel ashamed, then there will be no relief. Luckily, in my experience, most people want to offer help when someone is crying.

24:54And a 2011 study has found that these observers' behaviour might even change in a surprising way. There have been some researchers in Israel. They had a group of females. They made them cry with watching movies or just the recollection or a sad event or so. These tears were collected and given to a group of men. The men either sniffed the tears or they sniffed saline. A saline solution, which is regular salty water, was used as a control. And then they had to perform an aggression measure test. And it appeared that when they sniffed the saline, they showed more aggression than in the case of when they sniffed the tears.