# What is a tear?

An episode of [Science for Kids / Science's Not Boring: The Kids Science Podcast](https://invisiblenetwork.ai/podcast/1896928296), 16 Oct 2026, 11 min.

Audio: https://www.buzzsprout.com/2624612/episodes/19933858-what-is-a-tear.mp3

Did you know your body makes enough tears every year to fill half a bathtub? It’s true! In this episode, Mira and Finn dive into the wild, slightly slimy, and totally amazing science of tears! You might think crying is just salty water leaking from your eyeballs, but tears are actually a super-advanced biological shield. Discover the microscopic bacteria-chopping ninja enzymes hiding in your everyday basal tears, and find out why chopping onions unleashes a massive flood of reflex tears to wash away stingy gases. Plus, did you know humans are the only animals on Earth that cry emotional tears? We’ll explore how crying is actually a biological superpower that flushes out stress hormones like cortisol and helps your brain calm down after a big, messy cry. From tiny hidden drain holes in your eyelids to the real truth behind crocodile tears, you will never look at crying the same way again. Join us to find out exactly what happens when the waterworks start!

## Transcript

[0:00] SPEAKER_00: Welcome to Science is Not Boring by Kidopoly.com.
[0:04] SPEAKER_00: I'm Mira.
[0:05] SPEAKER_00: And I'm Finn.
[0:06] SPEAKER_00: A big hello to Sisters Sophie and Lila who asked, What it is and why do our eyes make them?
[0:13] SPEAKER_00: What a fantastic question.
[0:15] SPEAKER_00: And this episode is just for you two.
[0:18] SPEAKER_01: And a huge happy belated seventh birthday to Manal in Oakville, Canada.
[0:23] SPEAKER_00: If you haven't already, tap follow wherever you're listening so you never miss an episode.
[0:28] SPEAKER_00: Alright, Finn, get ready for this.
[0:31] SPEAKER_00: Did you know that every single year your body produces between 15 and 30 gallons of tears?
[0:38] SPEAKER_01: Wait, 30 gallons?
[0:40] SPEAKER_01: That's enough to fill half a bathtub.
[0:42] SPEAKER_01: But I don't cry that much.
[0:45] SPEAKER_00: You actually do.
[0:46] SPEAKER_00: You just don't notice it.
[0:48] SPEAKER_00: Today we are diving into the wild, wonderful, and slightly slimy science of tears.
[0:54] SPEAKER_01: Slimy?
[0:55] SPEAKER_01: Uh-oh.
[0:56] SPEAKER_01: What exactly is a tear anyway?
[0:59] SPEAKER_01: Isn't it just salty water leaking from our eyeballs?
[1:02] SPEAKER_00: Not quite.
[1:03] SPEAKER_00: A tear is actually a super advanced three-layered shield.
[1:07] SPEAKER_00: And you are making them right now.
[1:09] SPEAKER_00: Every time you blink, which happens about 15 to 20 times a minute, you spread a fresh batch of what scientists call basal tears over your eyes.
[1:19] SPEAKER_01: Fifteen times a minute?
[1:21] SPEAKER_01: That's thousands of blinks a day.
[1:23] SPEAKER_01: So these basal tears are like little windshield wipers for my eyes.
[1:28] SPEAKER_00: Exactly.
[1:29] SPEAKER_00: They are pumped out by the lacrimal glands, which are tiny almond-shaped organs tucked just above the outer corner of each eyeball.
[1:37] SPEAKER_00: And these tears aren't just water.
[1:39] SPEAKER_00: The inner layer is made of mucus.
[1:41] SPEAKER_00: Ew, mucus! Like snot on my eyeballs.
[1:46] SPEAKER_00: Yes, but it's crucial.
[1:48] SPEAKER_00: The mucus fastens the tear right to the surface of your eye, so it doesn't just slide off into your lap.
[1:54] SPEAKER_01: Okay, I guess that makes sense.
[1:57] SPEAKER_01: I wouldn't want my eyeballs drying out like raisins.
[2:00] SPEAKER_01: What's the next layer?
[2:02] SPEAKER_00: The middle layer is the thickest.
[2:04] SPEAKER_00: It's the aqueous layer, made mostly of water, salt, and special proteins.
[2:09] SPEAKER_00: It even contains an enzyme called lysozyme, which literally chops up bacteria to keep your eyes from getting infected.
[2:17] SPEAKER_01: Whoa! So I have microscopic bacteria-chopping ninjas swimming on my eyes right now.
[2:23] SPEAKER_00: You absolutely do.
[2:25] SPEAKER_00: And to top it all off, the outer layer is made of oil.
[2:29] SPEAKER_00: It's produced by tiny mybomian glands at the edges of your eyelids.
[2:34] SPEAKER_00: This oil acts like a blanket, stopping the watery layer from evaporating into the air.
[2:39] SPEAKER_01: So, mucus to make it stick, water with ninja enzymes to protect and clean, and oil to keep it locked in.
[2:47] SPEAKER_01: That's way more complicated than just water.
[2:50] SPEAKER_01: But wait, if these basal tears are always there, why do tears sometimes spill down our cheeks?
[2:57] SPEAKER_00: That brings us to tear type number two, reflex tears.
[3:01] SPEAKER_00: These are the emergency responders of the eye world.
[3:04] SPEAKER_01: Emergency responders.
[3:06] SPEAKER_01: Like when you get a piece of dust trapped under your eyelid and your eye starts watering like crazy.
[3:11] SPEAKER_00: Exactly.
[3:13] SPEAKER_00: When the nerves in your cornea detect an invader like dust, smoke, or a tiny bug, they send a panic signal to your brain.
[3:21] SPEAKER_00: Your brain shouts, flush it out, and the lacrimal glands unleash a massive flood of reflex tears.
[3:28] SPEAKER_00: They really do flood.
[3:30] SPEAKER_01: It's like turning on a fire hose.
[3:32] SPEAKER_01: Does this happen when you chop onions too?
[3:35] SPEAKER_01: My dad always cries when he makes soup.
[3:38] SPEAKER_00: Yes! Onions are famous for this.
[3:42] SPEAKER_00: When you slice an onion, you break open its cells, releasing a chemical called synpropenethyl S oxide.
[3:49] SPEAKER_00: It floats into the air as a gas.
[3:51] SPEAKER_01: That chemical name sounds serious.
[3:54] SPEAKER_01: What does it do to your eyes?
[3:55] SPEAKER_00: When that gas hits the watery surface of your eye, it creates a super mild acid.
[4:01] SPEAKER_00: It stings.
[4:03] SPEAKER_00: So your eye's defence system kicks in, pumping out loads of reflex tears to wash the acid away.
[4:09] SPEAKER_01: So wait.
[4:10] SPEAKER_01: When I cry reflex tears, why does my nose get all runny too?
[4:15] SPEAKER_01: Does the onion gas attack my nose?
[4:18] SPEAKER_01: Great question!
[4:19] SPEAKER_00: Your eyes actually have a tiny drainage system.
[4:22] SPEAKER_00: Look closely in the mirror at the inner corner of your eyelids, near your nose.
[4:27] SPEAKER_00: You'll see tiny holes called the lacrimal punctor.
[4:30] SPEAKER_01: Wait, I have drain holes in my eyelids.
[4:34] SPEAKER_01: Like a bathroom sink.
[4:36] SPEAKER_01: Yep.
[4:37] SPEAKER_00: Normally, your tears drain down those holes, into a sack, and then straight down a pipe into the back of your nose.
[4:44] SPEAKER_00: But when you make too many reflex tears, the sink overflows.
[4:48] SPEAKER_00: Some tears spill down your cheeks, and the rest flood down into your nose, mixing with your mucus.
[4:54] SPEAKER_01: Ew! So when I'm crying, my runny nose is actually my own tears flushing out through my nostrils.
[5:02] SPEAKER_01: That is completely gross.
[5:04] SPEAKER_01: But also kind of genius.
[5:06] SPEAKER_00: It's totally genius body mechanics.
[5:09] SPEAKER_00: But basil and reflex tears are just the beginning.
[5:12] SPEAKER_00: The third type of tear is what makes humans totally unique in the entire animal kingdom.
[5:18] SPEAKER_01: Wait, unique to humans?
[5:20] SPEAKER_01: Don't animals cry?
[5:21] SPEAKER_01: I swear my dog looks sad sometimes.
[5:24] SPEAKER_00: Animals definitely feel emotions, and they do make basil and reflex tears to clean their eyes.
[5:30] SPEAKER_00: But as far as science knows, human beings are the only creatures on Earth that produce emotional tears when we feel sad, happy, or overwhelmed.
[5:40] SPEAKER_01: Really?
[5:41] SPEAKER_01: Just us?
[5:42] SPEAKER_01: But why?
[5:43] SPEAKER_01: If reflex tears are for washing out dust, what are emotional tears washing out?
[5:48] SPEAKER_00: That is the exact question a biochemist named Dr.
[5:51] SPEAKER_00: William H.
[5:52] SPEAKER_00: Frey II asked in the 1980s.
[5:56] SPEAKER_00: He wanted to know if emotional tears were chemically different from reflex tears.
[6:01] SPEAKER_00: How do you even test that?
[6:03] SPEAKER_01: Did he just follow people around with a tiny bucket waiting for them to cry?
[6:07] SPEAKER_00: Almost.
[6:08] SPEAKER_00: He set up an experiment in a lab.
[6:11] SPEAKER_00: He had volunteers chop onions to collect their reflex tears in test tubes.
[6:16] SPEAKER_00: Then he had the same people watch super sad movies to collect their emotional tears.
[6:22] SPEAKER_01: Whoa, a professional crying lab.
[6:25] SPEAKER_01: What did he find under the microscope?
[6:27] SPEAKER_01: He discovered something mind-blowing.
[6:29] SPEAKER_00: Emotional tears are packed with different chemicals than onion tears.
[6:34] SPEAKER_00: They contain extra proteins and high levels of stress hormones, including one called cortisol.
[6:41] SPEAKER_01: Wait, so when you are stressed out, your body actually leaks the stress hormones out through your eyeballs.
[6:47] SPEAKER_00: Yes! Dr.
[6:48] SPEAKER_00: Frey's theory was that crying is literally an excretory process.
[6:53] SPEAKER_00: Just like exhaling removes carbon dioxide, shedding emotional tears flushes excess stress chemicals right out of your system.
[7:02] SPEAKER_00: It also releases endorphins, which are your body's natural painkillers.
[7:06] SPEAKER_01: That explains so much.
[7:09] SPEAKER_01: You know when you have a really big, messy cry, and afterwards you feel totally exhausted, but also kind of calm and relieved.
[7:17] SPEAKER_01: Exactly.
[7:18] SPEAKER_00: Your brain is getting a chemical reset.
[7:21] SPEAKER_00: Crying isn't a sign of weakness at all.
[7:24] SPEAKER_00: It's actually a biological superpower to help your brain calm down after a major event.
[7:30] SPEAKER_01: That is the coolest thing ever.
[7:32] SPEAKER_01: I am going to tell everyone that I'm just excreting excess cortisol next time I watch a sad movie.
[7:39] SPEAKER_01: Are there any other weird facts about tears?
[7:41] SPEAKER_01: Oh, definitely.
[7:43] SPEAKER_00: Have you ever heard the phrase crocodile tears?
[7:46] SPEAKER_01: Yeah.
[7:47] SPEAKER_01: Isn't that when someone pretends to be sad but they're faking it?
[7:50] SPEAKER_00: Right, but it comes from real biology.
[7:53] SPEAKER_00: Crocodiles actually do shed tears while they are eating their prey.
[7:58] SPEAKER_00: It has nothing to do with feeling sorry.
[8:00] SPEAKER_00: The muscles they use to chew are so powerful that they literally squeeze their laquimol glands, forcing reflex tears out of their eyes.
[8:09] SPEAKER_01: That is wild.
[8:11] SPEAKER_01: Imagine crying just because you're biting a really tough sandwich.
[8:15] SPEAKER_00: And here's one more beautiful fact.
[8:17] SPEAKER_00: An artist named Rosalind Fisher put different types of dried tears under a powerful microscope.
[8:24] SPEAKER_00: Because they have different levels of salts and minerals, they crystallise differently.
[8:29] SPEAKER_00: What do they look like dried up?
[8:31] SPEAKER_00: They look like intricate snowflakes, or maps of rivers and forests from above.
[8:36] SPEAKER_00: No two tears look exactly the same under the microscope.
[8:40] SPEAKER_00: Alright Finn, time for the quiz.
[8:42] SPEAKER_00: Are you ready?
[8:43] SPEAKER_01: Okay, I've got my bacteria chopping ninja brain ready.
[8:47] SPEAKER_01: Let's do this.
[8:48] SPEAKER_01: First question.
[8:50] SPEAKER_00: Approximately how many gallons of tears does a human produce in a single year?
[8:59] SPEAKER_00: Next one, what is the name of the tiny almond-shaped gland above your eye that produces these tears?
[9:09] SPEAKER_00: Question three.
[9:11] SPEAKER_00: Name the three layers that make up a basal tear.
[9:18] SPEAKER_00: Here's number four.
[9:19] SPEAKER_00: What specific stress hormone did Dr.
[9:22] SPEAKER_00: William Frey find in emotional tears?
[9:28] SPEAKER_00: Last question.
[9:30] SPEAKER_00: Which animals are the only ones known to cry emotional tears?
[9:37] SPEAKER_00: Great job! Let's see how you did.
[9:40] SPEAKER_00: The first answer is 15 to 30 gallons of tears per year.
[9:46] SPEAKER_00: For question two, it's the lacrimal gland.
[9:49] SPEAKER_00: Number three, the three layers are mucus, water and oil.
[9:54] SPEAKER_00: Question four.
[9:55] SPEAKER_00: He found the stress hormone cortisol.
[9:58] SPEAKER_00: And the final answer is humans, we are the only ones.
[10:03] SPEAKER_01: I am never going to look at crying the same way again.
[10:06] SPEAKER_01: It's basically a superpower that flushes out stress.
[10:10] SPEAKER_00: Totally! From onion gas to microscopes to tiny sink drains in our eyelids.
[10:16] SPEAKER_00: The human body is amazing.
[10:18] SPEAKER_01: Hey, if you love learning about tears today, please leave us a five-star review.
[10:23] SPEAKER_01: Just scroll down and tap the stars on your app and let us know if you shed any tears of joy learning with us.
[10:30] SPEAKER_00: Yes, and make sure to follow this show wherever you're listening.
[10:34] SPEAKER_00: Oh, and we have sister shows too.
[10:36] SPEAKER_00: History and philosophy's not boring, and maths is not boring.
[10:40] SPEAKER_00: Go give those a listen and a follow as well.
[10:43] SPEAKER_01: And if you want to shout out on the show, or just want to say hi, email us at hello at kidopoly.com.
[10:50] SPEAKER_00: Thanks for exploring with us today.
[10:52] SPEAKER_00: See you next time on Sciences Not Boring.
[10:56] SPEAKER_00: Bye everyone.

Shows are listed from Apple Podcasts' charts and directory, and Podcast Index where it is used. Every show and episode belongs to its publisher and plays from the publisher's own feed; this site hosts none of them.