Why do we cry? The three types of tears - Alex Gendler

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Whether we cry during a sad movie, while chopping onions, or completely involuntarily, our eyes are constantly producing tears. Alex Gendler tracks a particularly watery day in the life of Iris (the iris) as she cycles through basal, reflex and emotional tears.

Lesson by Alex Gendler, animation by The Moving Company Animation Studio.

Our story is about a girl named Iris.

Iris is very sensitive.

(Bird cawing)

So much that she is always in tears.

She cries when she's sad,

when she's happy,

(Godzilla roars)

and even tears up
when things just get to her.

She has special lacrimal glands
to make new tears

and special tubes, called lacrimal puncta,

to drain old ones away.

And she cries so much
that she goes through

ten ounces of tears per day,

thirty gallons a year!

In fact, if you look closely,

you'll see that she's crying
a little bit all the time.

The basal tears that Iris
constantly produces

form a thin coating of three layers

that cover her and keep
dirt and debris away.

Right next to Iris is the mucus layer,

which keeps the whole
thing fastened to her.

On top of it is the aqueous layer,

which keeps Iris hydrated,
repels invasive bacteria,

and protects her skin,
or cornea, from damage.

And, finally, there is the lipid layer,

an oily outer film that keeps
the surface smooth

for Iris to see through,

and prevents the other
layers from evaporating.

Normally, Iris goes about her day

without really noticing
the basal tears doing their thing.

That's kind of their whole point.

But one day, she meets a girl named Onion.

Iris is immediately smitten.

Onion looks gorgeous in her
bright purple jacket,

and she smells terrific.

So, Iris invites Onion
to her house for dinner.

But when she comes in
and takes off her jacket,

something terrible happens.

You see, when Onion's jacket is removed,

a chemical reaction happens,

converting the sulfoxides
that make her smell so great

into sulfenic acid,

which then becomes a nasty
substance with a long name:

syn-Propanethial S-oxide.

The gas stings Iris,
and suddenly, she can't help it,

she starts weeping uncontrollably.

These reflex tears are different
from the basal tears

that Iris is used to.

Because they're designed

to wash away harmful
substances, or particles,

they're released in much larger amounts,

and their aqueous layer
contains more antibodies

to stop any microorganisms
that may be trying to get in, as well.

Both Iris and Onion are devastated.

They know they can't continue
their relationship

if Iris is going to hurt and cry
every time Onion takes off her jacket.

So, they decide to break up.

As Onion walks out the door,
Iris stops crying.

And immediately starts again.

Only now, she's not crying
reflex tears but emotional tears.

When someone is either
too sad or too happy,

it feels like a loss of control,

which can be dangerous.

So, emotional tears are sent in
to stabilize the mood

as quickly as possible,

along with other physical reactions,

such as an increased heart rate
and slower breathing.

But scientists still aren't sure

exactly how or why the tears
themselves are helpful.

They may be a social mechanism
to elicit sympathy or show submission.

But some studies have also found

that emotional tears contain
higher levels of stress hormones,

such as ACTH and enkephalin,

an endorphin and natural pain killer.

In this case, emotional tears
are also directly calming Iris down,

as well as signaling
her emotional state to others.

Sorry things didn't work out
with Onion, Iris,

but don't worry.

As long as you have
all three kinds of tears

working to keep you balanced
and healthy, it will get better.

You'll see.