Science project

How to Cut an Onion Without Crying

Does cutting an onion leave you in tears? The cells of an onion contain sulfur compounds. Cutting the onion causes a chemical reaction to occur, releasing an enzyme that reacts with the tear ducts. There are many techniques that are said to reduce tear production while cutting but which one is the most effective?


  • Bag of Onions (8-10)
  • Candle
  • Knife (sharp & dulled)
  • Cutting board
  • Vinegar
  • Refrigerator
  • Goggles
  • Slice of white bread

Experimental Procedure:

  1. Place 1 onion in the refrigerator. We will use this later in our experiment.
  2. Using a dulled kitchen knife dice the onion. Using a dulled knife will be the control.
  3. Subjectively describe your tear production and record.

  4. Wait an hour before proceeding. This will allow time for your eyes to recover.
  5. Using a sharpened kitchen knife dice the onion.
  6. How does tear production compare to the control condition?
  7. Continue cutting the onion using the following methods, waiting an hour between each trial.

a.     Spray or coat the cutting board with vinegar and dice the onion.

b.    Take the onion out of the refrigerator and ensure the onion is chilled. Dice the onion.

c.     Put on a pair of airtight goggles such as swimming goggles. Dice the onion.

d.    Light a candle or turn on a gas burner. Dice the onion.

e.     Take a slice of white bread and bite on it so it hangs out of your mouth. Dice the onion.

f.     Cutting method: Cut the top of the onion (stem portion) off and slice towards the root but do not cut the root.

g.    Fill your kitchen sink of a large basin with water approximately 6" in depth. Submerge your cutting board and onion and cut the onion under water.

Terms/Concepts: Why do we tear up when cutting an onion? What happens to the onion chemically when we cut it?; What are some techniques to prevent this reaction?; What is the rationale behind each technique? How does it prevent tears?


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