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Why Do Onions Make Us Cry? | Amazing Facts for Children · The Curious Kidcast | Fun Facts and Curious Questions

• 0:37
  Hello, hello, hello, and welcome back to the Curious Kid cast,
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  where we answer the questions that make your brain itch in the
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  best possible way. I'm your host, Andy, and today
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  we're tackling a question that came all the way from a
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  brilliant listener named Sophie in Manchester, England.
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  Sophie wrote to us because she was helping her dad make his
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  famous spaghetti bolognese when something rather dramatic
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  happened. She started chopping an onion,
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  and within seconds she was crying like she'd just been told
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  her favorite TV show was cancelled forever.
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  Her dad thought it was hilarious.
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  Sophie thought it was extremely suspicious, so she asked us why
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  on earth do onions make us cry? Brilliant question, Sophie, and
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  I have to say, I've been there. Just last week I was making
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  onion soup and I looked like I'd been watching sad puppy videos
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  for three hours straight. My neighbor popped round, saw my
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  tear stained face, and asked if I was OK.
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  I had to explain. No, no, I'm fine, I'm just being
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  attacked by a vegetable. She backed away slowly.
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  But here's the thing. There's actually some seriously
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  cool science happening when you chop an onion.
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  We're talking chemistry, biology, and a vegetable that's
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  basically a tiny underground ninja.
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  So grab your safety goggles, metaphorical ones probably, and
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  let's dive in. Let's think about what an onion
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  actually is. It's not just sitting there in
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  your kitchen being innocent and round.
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  Oh no. That onion has been living
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  underground, minding its own business, and it's developed a
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  rather clever defense system. You see, onions can't run away
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  from danger. They can't grow teeth or learn
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  karate or call for backup. They're stuck in the ground.
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  So they came up with something much sneakier.
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  Chemical warfare. Inside every onion are these
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  tiny little storage compartments, like microscopic
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  cupboards filled with special chemicals.
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  While the onions intact, everything's fine.
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  The chemicals are kept separate, like ingredients that shouldn't
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  be mixed until you're ready to bake.
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  But the moment you cut, slice, or chop that onion, BAM, those
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  compartments burst open and the chemicals mixed together.
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  It's like accidentally combining the red wire and the blue wire
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  in a spy movie. Things are about to get
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  dramatic. Here's what happens step by
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  step. First, you cut the onion.
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  Your knife slices through thousands of tiny onion cells,
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  bursting them open like tiny water balloons.
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  Second, two substances that have been kept apart suddenly meet.
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  One's called aleanase, which is an enzyme, basically a protein
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  that speeds things up, and the other is something called
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  sulfenic acid. Third, these two react together
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  and create a gas. Now, this gas has an absolutely
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  bonkers name. Are you ready?
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  It's called sin proponethyl soxide.
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  Try saying that three times fast.
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  Actually, try saying it once. I'll wait.
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  Let's just call it the onion gas because I value my tongue and
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  its ability to pronounce normal words.
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  This gas is invisible, it's light, and it floats right up
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  from your chopping board into the air, heading straight for
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  your eyeballs like a tiny, irritating missile.
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  Now, your eyes are absolutely brilliant at their job.
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  They can see colors, shapes, movements, and they can help you
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  spot when someone's sneaking up behind you with a water balloon.
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  But they're also really, really sensitive.
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  They have to be, because they're exposed to the outside world all
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  day long. To protect themselves, your eyes
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  are covered in a thin layer of water tears that keeps them
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  clean and stops dust and germs from getting in.
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  It's like having tiny windscreen wipers running all the time.
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  But when the onion gas reaches your eyes, it dissolves in that
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  tear film and forms a mild acid. Now before you panic, it's a
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  very weak acid, not the kind that melts through metal in
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  cartoons, but your body doesn't know that.
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  Your eyes send an urgent message to your brain saying red alert,
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  we've been compromised. Deploy emergency tears
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  immediately and your tear glands, which are like tiny
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  factories sitting just above each eyeball, go into OverDrive.
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  They start pumping out extra tears to wash away the
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  irritating gas. That's why you end up looking
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  like you're sobbing over a vegetable, which, let's be
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  honest, is a pretty undignified way to spend an evening.
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  I once had to explain to my nephew why I was crying in the
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  kitchen and he said, Uncle Andy, are you sad?
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  Because the Onion had dreams. I didn't have the heart to tell
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  him it was just chemistry. For hundreds of years, people
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  knew onions made them cry, but they had no idea why.
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  Some people thought the smell was cursed.
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  Others believed onions released poisonous fumes.
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  A few people probably blamed witchcraft because back in the
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  old days people blamed witchcraft for pretty much
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  everything. My onion made me cry.
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  Must be a witch. My toast burned.
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  Definitely witches. It wasn't until the 20th century
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  that scientists finally figured out the real culprit.
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  Using microscopes and chemistry equipment, they discovered that
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  trachy enzyme and the gas it produces.
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  Fun fact, the gas is actually a sulfur compound, which is a
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  chemical element that also makes garlic smells so strong and
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  gives volcanoes that lovely rotten egg smell.
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  So basically, when you're crying over onions, you're experiencing
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  a tiny kitchen size volcano. You're welcome for that mental
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  image. But here's the good news.
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  Scientists and chefs have figured out some absolutely
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  brilliant ways to stop the tears.
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  Let me share my favorites and the science behind why they
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  work. First up, chill your onion.
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  Pop it in the fridge for about 30 minutes before you chop it.
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  Why does this work? Well, cold temperatures slow
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  down chemical reactions. It's like putting the onions
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  defenses in slow motion. Less gas escapes, which means
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  fewer tears. I keep a couple of onions in my
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  fridge just in case of cooking emergencies.
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  My friend once opened my fridge and said why do you have onions
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  next to your orange juice? I said trust me, it's science.
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  She still thinks I'm weird. Second, use a really sharp
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  knife. A dull knife crushes the onion
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  cells instead of cutting them cleanly, which releases way more
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  gas. A sharp knife makes a clean
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  slice through the cells. Fewer broken cells equals fewer
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  tears. It's like the difference between
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  carefully opening a bag of crisps versus just smashing it
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  with your fist. One method is definitely messier
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  than the other. 3rd, you can chop your onion underwater.
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  Some chefs actually do this in a bowl of water or under a gentle
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  running tap. The water dissolves the gas
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  before it can reach your eyes. Although I have to say, chopping
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  anything with a sharp knife while it's underwater feels a
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  bit like you're doing kitchen surgery.
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  It works, but you do look slightly ridiculous. 4th, turn
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  on a fan or your cooker hood if you have one.
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  The moving air blows the gas away from your face before it
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  can attack your eyeballs. The gas just wafts off into the
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  distance, probably to bother someone else.
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  Sorry neighbors. And 5th, my personal favorite,
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  wear goggles. Yes, swimming goggles.
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  Yes, in your kitchen. Yes, you'll look like you're
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  about to go scuba diving in a pot of soup.
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  But do you know what? They work brilliantly.
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  They form a tight seal around your eyes and keep all the gas
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  out. Plus, if anyone laughs at you,
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  you can say you're doing science, which you are.
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  Science doesn't always look cool, but it gets results.
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  Now let's talk about some absolutely wild onion facts that
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  you probably never knew and can use to impress people at dinner
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  parties or, you know, at school lunch.
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  Onions have been around for at least 5000 years.
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  Ancient Egyptians thought onions were magical and even buried
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  them with mummies as a symbol of eternal life.
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  Which raises the question, when the mummy woke up in the
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  afterlife, did they think, oh brilliant, someone packed me an
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  onion? History doesn't tell us ancient
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  Greek athletes used to eat onions before competitions
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  because they thought it made them stronger and faster.
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  Spoiler alert, it didn't. But they probably did smell
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  quite powerful. Imagine the ancient Olympics
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  with everyone reeking of onions. The discus throw must have been
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  particularly fragrant. Not all onions make you cry.
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  Some varieties, like Vidalia and Maui onions are much sweeter and
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  milder. They contain less of that tear
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  making enzyme so you can chop them without looking like you're
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  watching a sad movie. Where were these onions all my
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  life? Scientists in Japan actually
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  created a no tears onion. They use special breeding
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  techniques to stop the enzyme from forming the gas.
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  They called it the smiley onion, which is possibly the cutest
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  name for a vegetable ever. I want a whole kitchen full of
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  smiley onions. Here's something else that's
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  interesting. Not everyone cries the same
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  amount when they chop onions. You might have noticed this.
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  Some people can slice through a whole onion like they're robots
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  with no feelings. Others start crying before
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  they've even picked up the knife.
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  What's going on there? Well, it turns out everyone's
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  eyes are a bit different. Some people have more sensitive
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  tear ducts so their eyes react faster.
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  Others might just be standing in a better spot in the kitchen
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  where there's more air flow. And different types of onions
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  release different amounts of gas.
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  Red and white onions tend to be the tear jerkers, while sweet
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  onions are much gentler. So if someone teases you for
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  crying, you can tell them it's because you have superior onion
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  detecting abilities. You're basically a vegetable
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  superhero. Scientists absolutely love
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  studying onions because they're a simple way to understand plant
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  chemistry. Some researchers are even
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  looking at ways to use onion enzymes to create safer natural
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  chemicals for farming or medicine.
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  Meanwhile, plant breeders are working on even more tearless
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  onions. One day, crying over onions
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  might be something we only read about in history books.
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  Future kids will say, wait, you mean vegetables used to attack
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  people's eyes? That's mental.
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  Before we wrap up, I think it's time for a little quiz.
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  Let's see if you've been paying attention.
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  I'm going to ask you 3 questions and I'll give you 5 seconds to
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  think about each one. Ready.
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  Question one. What's the name of the enzyme in
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  onions that starts the chemical reaction when you cut them?
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  Is it a alinase, B lactose, or C photosynthesis?
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  The answer is A alinase. Well done if you got that.
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  Bonus points if you can actually pronounce it properly.
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  Question 2. Ancient Egyptians buried onions
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  with mummies because they believed onions symbolized what
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  was it A good luck, B eternal life, or C really good soup?
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  The answer is B eternal life. Although honestly, I think
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  really good soup would have been a solid choice too.
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  Question three. What's the nickname for the
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  special onion that scientists created that doesn't make you
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  cry? Is it A the happy onion, B the
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  smiley onion, or C the friendly onion?
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  The answer is B, the smiley onion.
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  I mean, it's adorable. I want to give it a hug.
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  So there you have it, curious listeners.
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  The next time you're in the kitchen and you start crying
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  over an onion, don't be embarrassed.
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  Be amazed. You're witnessing real chemistry
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  happening right in front of you. That little onion has spent
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  thousands of years evolving a brilliant defense system, and
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  every tear you shed is proof that nature is absolutely full
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  of surprises. And remember, if anyone laughs
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  at you for crying, just smile and say I'm not crying, I'm
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  doing science. Thanks so much for listening to
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  today's episode of The Curious Kid Cast.
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  A massive thank you to Sophie and Manchester for sending in
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  such a brilliant question. If you enjoyed this episode,
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  please share it with your friends and subscribe so you
• 11:52
  never miss another curious adventure.
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  And if you have a question you'd like us to answer, maybe about
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  why the sky is blue or why do we hiccup or why does chocolate
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  taste so good, head over to our website at curiouskidcast.com
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  and send it our way. We read every single one.
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  Until next time, stay curious, keep asking questions, and
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  remember the world is way more interesting when you wonder
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  about it. Hey.