What makes onions cause tears?

An irritating gas released when cut

Tears Quiz: Three Layers, Emotional Crying and Onions

This tears quiz reaches for a tissue to learn why we cry. Play 10 interactive questions on lacrimal glands above each eye, the three layers of the tear film, basal, reflex and emotional tears, how tears drain into the nose, the onion gas that sets off reflex tears, Darwin's thoughts on crying and why humans are the only animals known for emotional tears.

Start Tears Quiz

🎯 Daily Trivia Challenge • 🧠 10 Questions • ⏱️ 150 Seconds

Question 1 / 10 Time: 150s

Gland
Which glands make tears?
Layers
How many main layers does the tear film have?
Oil
What does the oily outer layer do?
Basal
Which tears constantly keep eyes moist?
Reflex
Which tears flush out irritants like smoke?
Onion
What makes onions cause tears?
Drain
Where do tears drain?
Salt
Why do tears taste salty?
Unique
Which animals are known for emotional tears?
Germs
Which tear ingredient helps fight bacteria?

Explanations: answer key for all 10 questions

Q1: Which glands make tears?
Answer: Lacrimal glands
They sit above each eye.
Q2: How many main layers does the tear film have?
Answer: Three
Oil, water and mucus.
Q3: What does the oily outer layer do?
Answer: Slows evaporation
It keeps the film from drying.
Q4: Which tears constantly keep eyes moist?
Answer: Basal tears
They coat the eye with each blink.
Q5: Which tears flush out irritants like smoke?
Answer: Reflex tears
They arrive in a rush.
Q6: What makes onions cause tears?
Answer: An irritating gas released when cut
It is called syn-propanethial-S-oxide.
Q7: Where do tears drain?
Answer: Into the nose
That is why crying makes a runny nose.
Q8: Why do tears taste salty?
Answer: They contain salts
Similar to other body fluids.
Q9: Which animals are known for emotional tears?
Answer: Humans
Other animals make reflex tears.
Q10: Which tear ingredient helps fight bacteria?
Answer: Lysozyme
It breaks down bacterial walls.

Why We Cry

Tears are made by lacrimal glands above each eye. The tear film has three main layers: an oily outer layer that slows evaporation, a watery middle layer and a mucus layer that helps it stick. Tears contain salts and lysozyme, an enzyme that helps fight bacteria.

There are three kinds of tears. Basal tears constantly keep the eyes moist with each blink. Reflex tears flush out irritants like smoke or the gas released when onions are cut. Emotional tears flow with sadness, joy or stress.

Tears drain through tiny ducts into the nose, which is why crying makes a runny nose. Many animals make reflex tears, but humans are the only animals known for emotional tears, a mystery Charles Darwin and many later scientists have pondered.

What This Quiz Teaches

Body science fans will enjoy these questions.

Where tears come from
Which layers they have
Which kinds exist
Why onions make us cry
What makes human tears unusual

Did You Know?

Chilling onions can reduce tears.
Dry eye happens when tears fall short.
Babies may cry without tears at first.
Blinking spreads the tear film.
Crying can feel relieving.