Why do humans cry? Understanding Tears and Eye Health
You've cried when you're sad, when you're happy, and maybe even when you cut an onion. But why do we cry — and what do tears actually do? Let's find out! Or watch the video from Dr. Krista Stapleton here!
What are tears made of?
Tears are made mostly of water, but they also have a little salt, some proteins, and oils mixed in. They come from tiny glands above each of your eyes called lacrimal glands — little factories that are always working, even when you're not crying.
In fact, your eyes make a very thin layer of tears all day long. It's only when they make a whole lot at once that you actually cry. So what causes tears to flow? That depends on which type of tear your body is making.
Three types of tears — yep, three!
Not all tears are the same. Scientists have found there are actually three different kinds of tears, each with a different job:
Basal tears — The always-on kind. They keep your eyes wet, clean, and protected every single second of the day.
Reflex tears — These show up when something irritates your eye — like smoke, wind, dust, or that onion you just cut!
Emotional tears — The ones that come when you feel a big feeling — sadness, joy, frustration, or even pride.
What do tears actually do for your eyes?
Your eyes are one of the most sensitive parts of your body. Tears act like a superhero team that protects them 24/7.
They keep your eyes moist. Without tears, your eyes would dry out — kind of like how your lips crack when they're dry.
They wash out bad stuff. When a speck of dust or an eyelash gets in your eye, reflex tears rush in to flush it out.
They fight germs. Tears contain something called lysozyme — a germ-fighting ingredient that kills bacteria before they can make your eyes sick.
They bring nutrients to your eye. The front of your eye doesn't have blood vessels, so it gets its oxygen and nutrients straight from your tears. Your eyes are literally using tears to stay healthy!
Fun fact: Humans are the only animals on Earth known to cry because of feelings. Other animals may produce tears to protect their eyes, but emotional crying appears to be a uniquely human experience!
Why do we cry when we have big feelings?
This is the really interesting part. When something big happens — you lose a game, someone is mean to you, or you're bursting with happiness — your brain gets very activated. It sends signals through your nervous system, and those signals trigger your tear glands to produce emotional tears.
Scientists think emotional crying actually helps your body calm down. Crying releases chemicals in your brain that act like natural stress relievers. After a good cry, many people feel less tense — even if nothing has changed.
Crying is also a signal to other people. When someone sees you crying, they often want to help or comfort you. So tears are a way of saying “I need some support right now” without using any words at all.
The science of crying: Emotional tears are actually different from regular eye-lubricating tears. They contain higher levels of cortisol — the stress hormone — that your body is trying to get rid of. So crying might literally be your body releasing built-up stress, like opening a pressure valve!
Why do we cry when we laugh really hard?
You've probably had this happen: something is SO funny that you start tearing up. When you laugh very hard, your face scrunches up and your eyes squeeze — that physical pressure pushes tears out of your tear glands, even though nothing is sad. Your body also gets a big rush of emotion, and tears just come along for the ride.
Why do onions make you cry?
When you cut an onion, it releases a gas into the air. That gas floats up to your eyes and turns into a mild acid when it mixes with your tears. Your eyes immediately go into emergency mode and produce lots of extra reflex tears to wash the irritant away. Want a tip to stop it? Chill your onion in the fridge before cutting — the cold slows down the gas release.
Is crying good for you?
Yes! Crying gets a bad reputation sometimes, but science says it's actually a healthy and normal response. It protects your eyes, helps your body release stress chemicals, and signals to people around you that you might need support.
There's nothing weak about crying. Understanding your own feelings well enough to cry about them is a pretty brave and self-aware thing to do.
A day in the life of your tears
Your eyes are busy from the moment you wake up. Here's what your tears are doing all day long — even when you don't notice them.
6:30 AM
Basal
You wake up — eyes snap into action
The second your eyes open, your lacrimal glands start pumping out a thin film of basal tears. This happens automatically — your body knows your eyes need moisture to work. Without this thin layer, your eyes would feel like sandpaper within minutes.
7:10 AM
Reflex
You step outside into cold, windy air
A gust of cold wind hits your face. Your eyes detect the irritation and immediately flood with reflex tears to protect themselves. These tears contain extra lysozyme, a germ-fighting ingredient, so even the wind triggers a mini defense response. It happens to everyone — every single day.
9:00 AM
Basal
Staring at a screen — blinking slows down
Whether it's a work computer, a phone, or a TV, when you stare at a screen you blink far less — sometimes only 3–4 times a minute instead of the normal 15–20. Less blinking means less spreading of tear film, and your eyes start to dry out. That tired, scratchy feeling after a long screen session? That's your tear film breaking down.
12:15 PM
Reflex
Cutting onions at lunch
Onion gas drifts into your eyes and turns into a mild acid on contact with your tear film. Your nervous system fires a massive surge of reflex tears to flush it out. These have nothing to do with feelings — it's pure chemistry.
3:45 PM
Emotional
A sad video pops up on your phone
Your brain processes a powerful emotional signal and releases a hormone called prolactin. This tells your lacrimal glands to ramp up production. Emotional tears contain stress hormones like cortisol that your body is trying to release. Crying is literally your body flushing out built-up stress.
7:30 PM
Emotional
Laughing so hard at a movie
Your face scrunches and your eyes squeeze shut from laughing — that physical pressure pushes tears out. Big positive emotions also activate the same brain circuits as sadness. Happy crying is real crying — just triggered differently.
10:30 PM
Basal
You fall asleep — tear production slows
When your eyes close for the night, tear production slows right down. Your eyelids trap moisture inside. This is why your eyes feel crusty in the morning: dried-up basal tears and tiny bits of dust collected overnight. Your tear glands worked a full 16-hour shift.
Did you know? Your eyes produce around 15–30 tiny droplets of basal tears every hour — up to 10 oz of tear fluid a year just to keep your eyes moist. Most drain quietly through tiny holes called puncta into your nose. That's why you get a runny nose when you cry!
Frequently asked questions about crying and tears
Why do humans cry but most animals don't?
Humans cry for emotional reasons because we have a highly developed brain that processes complex feelings like grief, joy, and empathy. Most animals produce basal tears to keep their eyes moist, but emotional crying appears to be unique to humans. Scientists believe it may have evolved as a social signal — a way to show vulnerability and ask for help from others nearby.
What causes tears to fall — what's the science?
Tears are produced by lacrimal glands above each eye. When something triggers them — emotion, irritation, or your blink reflex — these glands release more fluid than usual. When there's too much to drain through the tiny tear ducts in the corners of your eyes, the overflow spills out as tears down your cheeks. That's the science of crying in a nutshell!
Is crying good for your mental health?
Many researchers think so! Emotional tears contain stress hormones like cortisol, so crying may literally help your body remove built-up stress chemicals. After crying, many people report feeling calmer and more relaxed. It also communicates your emotional state to others, which can bring comfort and social support — both important for mental wellbeing.
Why do onions make you cry?
When you slice an onion, it releases a chemical called syn-propanethial-S-oxide into the air. When this gas reaches your eyes, it reacts with moisture to form a mild sulfuric acid. Your eyes detect the irritation and your brain triggers a flood of reflex tears to rinse it away. The tears have nothing to do with emotions — it's purely your eye's defense system at work!
Why do we cry when we're happy?
Happy tears happen because strong positive emotions — like overwhelming joy, pride, or relief — activate the same part of the brain that processes sadness. Your nervous system can get so flooded with intense feeling that it needs a release, and tears are one of the body's ways of letting that out. So happy crying is just your brain managing a very big emotion!
Do tears have any healing properties?
Yes, in a way! Tears contain lysozyme, an enzyme that can break down the cell walls of certain bacteria, helping to protect your eyes from infection. Basal tears also carry oxygen and nutrients to the surface of your eye, which doesn't have its own blood supply. So your tears are constantly doing quiet healing and protective work, even when you're not crying at all.
Why do some people cry more easily than others?
How easily someone cries is influenced by genetics, hormones, personality, and life experiences. Research suggests that people with higher empathy tend to cry more easily. Hormones also play a role — prolactin is linked to emotional crying. Culture and upbringing matter too: people raised in environments where expressing emotion is encouraged may cry more freely than those taught to hold it back.
Have questions about your eyes? The team at West Georgia Eye is here to help. Whether it's dry eyes, irritation, or just curiosity — we'd love to see you. → Book your appointment today at West Georgia Eye Your eyes work hard for you every single day — let us help take care of them.
“Tears are words that the heart can't say — but your body figured out how to say them anyway.”