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Our story is about a girl named Iris.

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Iris is very sensitive.

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(Bird cawing)

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So much that she is always in tears.

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She cries when she's sad,

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when she's happy,

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(Godzilla roars)

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and even tears up
when things just get to her.

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She has special lacrimal glands
to make new tears

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and special tubes, called lacrimal puncta,

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to drain old ones away.

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And she cries so much
that she goes through

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ten ounces of tears per day,

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thirty gallons a year!

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In fact, if you look closely,

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

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The basal tears that Iris
constantly produces

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form a thin coating of three layers

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that cover her and keep
dirt and debris away.

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Right next to Iris is the mucus layer,

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which keeps the whole
thing fastened to her.

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On top of it is the aqueous layer,

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which keeps Iris hydrated,
repels invasive bacteria,

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and protects her skin,
or cornea, from damage.

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And, finally, there is the lipid layer,

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an oily outer film that keeps
the surface smooth

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for Iris to see through,

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and prevents the other
layers from evaporating.

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Normally, Iris goes about her day

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without really noticing
the basal tears doing their thing.

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That's kind of their whole point.

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But one day, she meets a girl named Onion.

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Iris is immediately smitten.

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Onion looks gorgeous in her
bright purple jacket,

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and she smells terrific.

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So, Iris invites Onion
to her house for dinner.

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But when she comes in
and takes off her jacket,

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something terrible happens.

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You see, when Onion's jacket is removed,

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a chemical reaction happens,

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converting the sulfoxides
that make her smell so great

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into sulfenic acid,

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which then becomes a nasty
substance with a long name:

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syn-Propanethial S-oxide.

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

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she starts weeping uncontrollably.

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These reflex tears are different
from the basal tears

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that Iris is used to.

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Because they're designed

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to wash away harmful
substances, or particles,

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they're released in much larger amounts,

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and their aqueous layer
contains more antibodies

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

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Both Iris and Onion are devastated.

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They know they can't continue
their relationship

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

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So, they decide to break up.

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As Onion walks out the door,
Iris stops crying.

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And immediately starts again.

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

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When someone is either
too sad or too happy,

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it feels like a loss of control,

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which can be dangerous.

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So, emotional tears are sent in
to stabilize the mood

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as quickly as possible,

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along with other physical reactions,

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such as an increased heart rate
and slower breathing.

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But scientists still aren't sure

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exactly how or why the tears
themselves are helpful.

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

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But some studies have also found

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that emotional tears contain
higher levels of stress hormones,

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such as ACTH and enkephalin,

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an endorphin and natural pain killer.

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

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as well as signaling
her emotional state to others.

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

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but don't worry.

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As long as you have
all three kinds of tears

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

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You'll see.