Why Onions Make You Cry (Pyaz Tears) and Tricks That Really Work
Onions make you cry because cutting them releases a sulphur gas that drifts up and irritates your eyes, and the tricks that genuinely help are a chilled onion, a sharp knife, leaving the root end for last and cutting under a running chimney or fan. Bread in the mouth and a lit candle? Mostly hope. Here’s why.
Quick facts
- The culprit: a sulphur gas made in seconds when onion cells break.
- Works well: 30 minutes in the fridge, a sharp knife, airflow, goggles.
- Works a little: root end last, halving under running water.
- Weak or none: bread or a spoon in the mouth, a candle, chewing gum.
- Harmful? No. The tears wash it away. Don’t rub your eyes with onion hands.
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Why do onions make you cry?
A whole onion doesn’t sting. Sniff it. Nothing.
The trouble starts when the knife breaks the cells. Inside each onion cell sit sulphur-containing compounds, and in a separate compartment sits an enzyme called alliinase (the onion enzyme). When cutting tears the cell open, the enzyme grabs those sulphur compounds and changes them, and a second enzyme turns the result into a light, fast-moving gas with a long name, syn-propanethial-S-oxide, which chemists simply call the tear factor. It floats up, lands on the wet surface of your eye, and the nerves there read it as an irritant. Your eye does the sensible thing and floods itself with tears to wash it off.
So crying over onions is a reflex. No harm done.
This whole setup is the onion’s defence against being eaten in the field, because an animal that bites into a raw bulb gets a sudden burst of sharp, stinging gas in its nose and eyes, and it quickly learns to leave onions alone and go and dig up something milder instead. Garlic runs a similar enzyme trick, which is why crushed lehsun smells so much stronger than a whole clove; we covered that side in raw vs cooked garlic.
Heat switches the tear factor off, which is why frying onions in the karahi never makes anyone cry.
The tricks that actually work, rated
- Chill the onion first (works well). Put whole, peeled onions in the fridge for 30 minutes, or the freezer for 10 to 15 minutes. Cold slows the enzyme down and also keeps the gas from rising off the board so readily, which means far less of it ever reaches your eyes while you work through the pile. Don’t forget them in the freezer; a frozen onion goes mushy and is hard to cut safely.
- Use a sharp knife (works well). A sharp blade slices cleanly through cells. A blunt one crushes and tears far more of them, so more gas is made. Safer, too.
- Cut under airflow (works well). Chop beside a running chimney hood, an exhaust fan or an open window, or put a table fan behind you blowing across the board. The gas is carried away. Simple.
- Leave the root end for last (helps a little). Halve the onion from top to root, peel it, and slice with the root still holding the layers together. The root area is said to carry more of the tear-making compounds, and keeping it whole also makes neat dicing easier.
- Wear goggles (works very well). Swimming goggles or close-fitting kitchen goggles seal the gas out completely. They look silly. They work. Many contact lens wearers notice fewer tears too.
- Halve under running water (helps a little). Rinsing the cut halves washes some of the compounds off the surface. Only do this for halving, not fine chopping; wet onion slides on the board.
A food processor or a closed hand-pull chopper is the best friend of anyone making a big pot of biryani or qorma. The gas is trapped in the bowl, so just wait a moment before you open the lid and lean over it, or you get the whole trapped cloud in one go.
Big batch days
For 1 kg of onions for bhunao, peel them the night before, bag them and chill. Next day, slice with a sharp knife near the chimney with it running on high. Most people who try this combination find the tears drop from a flood to a sniffle.
Myths rated: bread, candle, spoon and gum
Onion hacks spread fast, from forwarded WhatsApp videos to advice shouted across the kitchen at a wedding, because every single person who has ever made a pot of salan has cried over an onion and wants the tears to stop, so here is an honest look at the popular ones. Short verdicts.
| Trick | Verdict | Why |
|---|---|---|
| Bread or roti in the mouth | Weak | May make you breathe through the mouth; the gas still reaches your eyes. |
| Lit candle nearby | Weak | The small draft is too gentle to clear the gas. An open flame by the chopping board is a hazard. |
| Metal spoon in the mouth | None | No known way for it to act on a gas at eye level. |
| Chewing gum | Weak | Same as bread: a small mouth-breathing effect at best. |
| Salt or vinegar on the board | Weak | Touches only the cut surface, not the gas already in the air. |
None of these hurt you, apart from the candle, so if one seems to help you there’s no harm in keeping it as a habit, but don’t rely on it alone before a 2 kg biryani prep when a fan, a cold onion and a sharp knife would do far more.
Why some onions sting more than others
Onions differ. A lot. Sharp, pungent onions, which include many of the red and pinkish desi varieties, make more of the sulphur compounds, so they sting more and taste hotter raw. Sweet onions grown in low-sulphur soil sting less and suit salads. Onions that have been stored for months, especially in a warm room or a hot store cupboard next to the stove in summer, often get sharper as they slowly dry out, so the last few from an old sack can sting noticeably more than the fresh ones you bought at the start of the season. Spring onion (hara pyaz) greens? Barely any sting.
A stinging onion isn’t a bad onion. If you want tips on spotting rot and black mould, see red vs white onion and how to spot a rotten one.
What cooking and soaking do to the sting
Heat destroys the onion enzyme. Fully. That’s why frying onions until golden (bhunao) makes them sweet instead of sharp: the stinging compounds are gone and the natural sugars caramelise.
For raw onion in kachumber or with daal, soaking sliced onion in iced water for 10 to 15 minutes, or in water with a squeeze of lemon, washes away some of the sharp sulphur compounds and makes the rings crisp. A pinch of salt rubbed in and rinsed off does something similar. Milder taste. Same nutrition.
Onion tears are harmless, but don’t rub your eyes with onion-coated fingers; wash your hands with soap first. If your eye keeps burning, looks very red or your vision is blurred after rinsing with clean, cool running water for several minutes, see a doctor or an eye clinic the same day. Contact lens wearers should wash hands before touching lenses. Children should be kept away from sharp knives and chopping; a teenager learning to cut should start with a chilled onion held with a “claw” grip. Never leave a candle or open flame by a chopping board.
Onion and tears: questions people ask
Why do onions make you cry?
Cutting breaks onion cells and lets an enzyme turn sulphur compounds into a light gas. The gas reaches your eyes, irritates the nerves there and makes tears flow to wash it out.
How do you cut onions without crying?
Chill the onion for 30 minutes, use a sharp knife, cut beside a running chimney or fan, and leave the root end for last. Goggles stop the tears almost completely.
Does putting onion in the fridge stop tears?
Yes, it helps a lot. Cold slows the enzyme and keeps the gas from rising as quickly. Thirty minutes in the fridge or 10 to 15 minutes in the freezer is enough.
Does holding bread in the mouth stop onion tears?
Not much. It may nudge you to breathe through your mouth, but the gas still drifts up to your eyes. Airflow and a chilled onion work far better.
Does a candle stop onion tears?
There’s little reason to think so. The draft from a candle is tiny, and an open flame beside a knife and chopping board is a hazard.
Are onion tears bad for your eyes?
No. The tears are a normal reflex that washes the irritant away. See a doctor only if burning, redness or blurred vision continues after rinsing with clean water.
Why don’t cooked onions make you cry?
Heat destroys the enzyme that makes the tear gas. Once onions hit hot oil, the stinging stops and they turn sweet as they brown.
Which onion makes you cry the most?
Sharp, pungent onions, including many red desi varieties, make the most tear gas. Sweet onions and spring onions sting much less.
Do contact lenses stop onion tears?
Many wearers find they tear up less, because the lens covers part of the eye. Wash your hands well before touching your lenses after cutting onions.
How do you take the sharpness out of raw onion for salad?
Soak sliced onion in iced water for 10 to 15 minutes, or rub with a pinch of salt and rinse. The rings stay crisp and taste milder.
More honest explanations of what happens on your chopping board live in Kitchen Science, Honestly.