Topics Food and drink

Why do onions make you cry?

Onions make you cry because cutting one breaks open its cells and mixes chemicals that were kept apart. An enzyme then helps turn a sulfur compound into a volatile gas that drifts up to your eyes. The nerve endings on the surface of your eye sense the irritant, and your tear glands respond by flushing it out. You are not sad. Your eye is rinsing itself.

What makes it interesting is how deliberate it looks. The onion is a plant with no way to run, and this reaction works like a chemical alarm that only goes off when something damages it. It is also why the same vegetable can be sharp and harsh raw, and sweet and mellow after a long time in a pan. Many familiar kitchen tricks, like chilling the onion or using a sharp knife, are really guesses about this chemistry, and some work better than others. Scientists have also found that the details of the reaction are more complicated than early textbooks suggested.

An episode would walk through the reaction step by step, then test the popular fixes against what we actually know. bre is an app whose hosts are AI, so they can be wrong, and the episode says where the science is settled and where it is not. You can press Talk and ask your own question mid-episode.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

  1. What your eye is actually doingTears are a reflex, not an emotion. Nerve endings on the surface of the eye detect an irritant, and the tear glands flush it away.
  2. A reaction waiting to happenInside an intact onion, the ingredients sit in separate places. Cutting the cells lets an enzyme meet a sulfur compound and start the chain.
  3. The gas that reaches your eyesThe reaction ends in a small, volatile molecule that floats up from the board. Why it irritates is a matter of how it reacts with moisture and nerve sensors.
  4. Why would a plant do this?The likely answer is defense against animals and pests. That is a sensible explanation, though it is an inference about evolution, not something anyone watched happen.
  5. Do the kitchen tricks work?Chilling, sharp knives, fans, goggles and running water all get tested against the chemistry. Some have good reasoning behind them and others are mostly folklore.
  6. From sharp to sweetHeat changes the sulfur compounds, which is part of why cooked onions taste so different from raw ones. Caramelizing adds a second story about sugars.
  7. Onions that do not make you cryBreeders have developed milder varieties, and the difference is a matter of chemistry and growing conditions. The episode covers what is known and what is still debated.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Tess. Both are AI; this is written by AI, as every bre episode is.

  1. breAI host

    Here's a question I've never actually stopped to ask. I'm standing at a cutting board, nothing sad is happening, and my eyes are streaming. What is the onion doing to me?

  2. TessAI host

    Okay, but real talk. It feels personal. You're just making dinner and the vegetable fights back.

  3. breAI host

    It sort of is fighting back. An onion can't run away, so it keeps a chemical defense ready, and it only switches on when the onion gets damaged.

  4. TessAI host

    So the knife is the trigger.

  5. breAI host

    Right. Inside the onion, a few ingredients are kept in separate spots. Slice through the cells and they mix, and that starts a short chain of reactions.

  6. TessAI host

    And the end of the chain is a gas that floats up into my face.

  7. breAI host

    Yes. Your eye senses it as an irritant, and the tears are just a rinse. Nothing to do with feelings.

  8. TessAI host

    Good. Then I want to know which of the tricks actually work, because I've tried the bread-in-your-mouth one and I'm not sure it did anything.

Questions people also ask

Is crying from onions harmful?
For most people it is a short, harmless irritation. The tears wash the irritant away and the stinging fades once you step back or the gas clears. If your eyes stay painful or red, that is a question for a doctor, not an AI-hosted podcast.
Why do some onions make you cry more than others?
Onions differ in how much of the relevant sulfur compounds they hold, and that depends on variety and growing conditions such as the soil. Freshness may matter too. The exact differences are still being studied, so be wary of simple rules.
Do chilling an onion or using a sharp knife help?
There is reasonable logic for both. Cold may slow the reactions and a sharp knife damages fewer cells, so less gas escapes. Neither fully stops it, and some other tricks are mostly folklore. An episode compares them with what is known.
Why do cooked onions not make you cry?
Heat changes the compounds involved and stops the enzyme that drives the reaction, so far less irritant forms. That is also part of why cooked onions taste milder and sweeter than raw ones.

Related topics

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bre’s hosts are AI, and every episode is generated, so they can be wrong: check anything that matters. This page outlines what an episode would cover. It is for interest and learning, not medical, financial or legal advice.