Chopping onions is an essential skill in the kitchen, but it often leads to tears streaming down your face. If you’ve ever wondered why onions specifically cause this reaction, you’re not alone.

Let’s explore the science behind why onions make you cry and reveal tips to prevent stinging, watery eyes while cooking


Onions contain compounds that irritate the eyes and stimulate the lacrimal glands to produce tears as a defense response. When an onion is cut, enzymes within the plant cells break down sulfur-containing amino acids and generate a volatile gas called sync-propanetriol-S-oxide. This gas wafts towards your eyes and triggers a nerve reaction, making you cry.

Although an annoying phenomenon, the crying response shows the sophisticated defense mechanisms of the onion plant and complex physiology of human tear production.

By understanding the science and chemistry behind this reaction, we can discover techniques to outsmart the onion’s defenses and maintain clear, dry eyes while chopping.

Let’s dive deeper into why onions evoke such a strong response and how you can prevent tearful cooking?

“I have to be careful cutting onions. I start to cry, and I forget what I’m chopping.”

Barbara Walters

Why Do Onions Make You Cry?

Onions contain a sulfur-based irritant that stimulates a neural reflex to generate tears when chopped.

But how exactly does this irritant form and affect the eyes?

Onion Chemistry Produces a Volatile Gas

When an onion is cut, cells are broken open allowing enzymes to mix with sulfur-containing amino acids. This produces sulfonic acid which quickly rearranges itself into sync-propanetriol-S-oxide, the tear-inducing volatile gas.

The Gas Triggers a Nerve Response

When sync-propanetriol-S-oxide wafts towards your eyes it activates nerve endings located on the cornea and conjunctiva. This trigeminal nerve stimulation sends a pain response to the brain.

Brain Signals Increase Tear Production

Your brain interprets the nerve signal as an irritant in the eye, prompting a reflex to wash it out. It sends impulses to stimulate lacrimal glands around the eyelids to secrete more tears than normal.

Tears Wash Away the Irritant

The extra tears generated flush out the gaseous irritant from the surface of the eyes. By keeping tear production elevated, the body aims to dilute and remove the painful stimulus. This is why cutting many onions causes copious crying over an extended time.

So in summary, enzymes produce a tear-inducing sulfur gas when onions are cut, which triggers the body’s reflex system to protect the eyes by secreting more tears to flush out the irritant. Pretty clever system!

“The onion itself is a contemplative vegetable, indeed; altogether to my mind displaying a greater amount of general sagacity than any vegetable I know of.”


What Factors Influence Onion Tears?

Not all onion encounters end in tears. Several factors influence how much crying occurs, including:

Onion Type and Sulphur Content

Some onion varieties contain more Sulphur compounds and create more gas when cut. Yellow, white, and Spanish onions tend to sting the most. Sweet onions like Vidalia are bred to be lower in the tear-inducing compounds.

Damage to Onion Cells

More tearing occurs when extensive cell damage allows enzymes to widely mix with sulfur amino acids. Finely chopping or pureeing releases more gas than slicing intact rings.

Exposure Time and Proximity

Standing close to the cut onions allows more direct exposure to the vapor, rather than it dispersing in the air. Prolonged prep also increases exposure over time.

Fan Direction

If you point a fan away from the onions, it can direct the gas away from your face. Fans blowing towards you worsen tearing.

Individual Sensitivity

People have varying levels of sensitivity. The elderly produce fewer tears and are more prone to irritation. Onion vapors also bother some individuals more than others.

So in general, high Sulphur containing onions chopped finely right under your nose for long periods create the worst tear-inducing potential. Milder onions sliced briefly at a distance cause less reaction.

“Cutting onions is like visiting different emotional states—one minute you’re joyful, the next you’re grieving.”

Erin McKean

Tips and Hacks to Prevent Onion Tears

Now that we know why onions make us cry, here are some scientifically-proven ways to reduce onion tears and keep chopping comfortably:

Use a Sharp Knife

A sharper knife damages fewer onion cells, producing less tear gas. Use a freshly honed blade and slice cleanly rather than crushing and tearing cell walls.

Chill the Onion

Lower temperatures slow the enzyme reaction that creates the gas. Refrigerate onions for 30-60 minutes before cutting to substantially limit tears.

Cut Under Running Water

Rinsing the onion dilutes and flushes away the gas before it reaches your eyes. Doing this prevents the buildup of irritants.

Place Bread in Mouth

Chewing bread while chopping absorbs some sulfur compounds before you fully inhale them. Just don’t choke on the bread!

Use a Fan

Direct a fan to blow the gas away from your face as you chop. This diffuses it and keeps your eyes away from the concentrated fumes.

Wear Onion Goggles

Special goggles designed for cutting onions block the vapors from reaching your eyes. Less fancy options like swim goggles work too.

So by using sharp knives, chilling onions, rinsing, fan blowing, and goggles, you can beat the onion’s tear-inducing defenses and comfortably chop away without crying. No more painful, puffy onion eyes!

The Chemistry of Onion Tears vs Emotional Crying

Interestingly, the tears induced by onions have a different chemical makeup than emotional tears. Onion tears are mostly water with a small amount of proteins, lipids, and mucin.

Emotional tears contain more biological substances like the protein-based hormones prolactin, adrenocorticotropic, and leucine enkephalin, which act as natural painkillers.

So while chopping onions triggers a neural reflex and waters your eyes, emotional crying serves several biological functions:

  • Removes stressful hormones from the body
  • Lowers cortisol and bodily arousal
  • Releases endorphins that relieve pain
  • Improves mood through inner chemical balance

This means stinging onion tears are quite different from cathartic emotional tears! Both are natural physical responses, but they serve separate purposes.

Why Do Onions Make Some People Cry More?

While onions make most people tear up, some individuals cry dramatically more than others when chopping. A few reasons certain people react more strongly include:

  • Increased sensitivity to sulfur compounds
  • Greater number of trigeminal nerve endings
  • Higher levels of the crying-stimulating enzyme lachrymatory factor synthase
  • Reduced tear drainage from the eye that allows irritant buildup

So in essence, differences in nerve sensitivity, enzyme levels, and tear drainage capability cause some to experience more extreme crying when slicing onions. However, breathing techniques, proper ventilation, and wearing goggles can help mitigate excessive tearing.

Can Onion Tears Lead to Any Harm?

Besides possible mild and temporary eye irritation, onion vapors do not cause any serious damage or long-term effects on vision or eye health. However, onion juices can potentially carry foodborne illnesses.

So be sure to wash hands, utensils, and cutting boards after prepping onions to prevent bacteria transfer. Proper knife skills that don’t crush onions can also lower this risk.

Someone Said:

It’s not the onions that will make your eyes water in times of sorrow, but sorrow that will make your eyes water over the onions.”

Mehmet Murat

Overall, while onion vapors may cause some transient stinging and reflexive tears, they will not harm your eyes or permanently affect sight.

Onion tears are mostly just a nuisance without lasting consequences. Following proper food safety practices prevents any harmful spread of illnesses through onion juices.

Why Do Some People Cry More Easily Generally?

Beyond just onions, some individuals have a lower threshold for crying from emotional triggers or eye irritants. A few factors that can contribute to being a frequent crier include:

  • Differences in tear gland structure – Some have larger glands.
  • Hormone levels – More prolactin and oxytocin.
  • Gender – Women’s tear glands are anatomically different.
  • Personality – Those more prone to emotion or empathy.
  • Prior trauma – Past pain lowers the crying threshold.

So biology, hormones, and psychology all play a role in tearfulness. If you cry often cutting onions or in life, don’t feel bad – embrace it as part of what makes you human!


Onion TypeTear Factor
Yellow OnionHigh
White OnionHigh
Red OnionMedium
Sweet OnionLow


Tearing up when you chop onions is an annoying but harmless experience shared by many home cooks. By understanding the science behind how sulfur compounds trigger an irritated nerve and reflexive tear response, we can find ways to outwit the onion’s defenses through proper techniques and tools.

Although onion tears temporarily sting, they cause no lasting damage and differ biologically from emotional crying. So don’t let onions keep you from cooking.

With the right preparation, you can chop onions to your heart’s content without shedding a single tear!

Chopping fresh, raw onions releases a volatile sulfur-containing gas that irritates eyes and triggers a tearing reflex. By understanding the science involved, we can prevent onion tears through proper chilling, knife skills, ventilation and eye protection.

While onion vapors may temporarily sting, they do not cause any lasting harm or damage vision. So don’t let watery eyes deter you from cooking with aromatic onions.

With the right knowledge and preparation, you can chop onions tear-free and enjoy their flavor in your cooking!

Frequently Asked Questions

Q: Why do some onion types make you cry more?

A: Onions higher in sulfur compounds produce more irritating gas when cut, like yellow or white onions. Sweet onions are bred to be lower in these.

Q: Does refrigerating onions help prevent crying?

A: Yes, chilling onions slows the enzymatic reaction that produces the tear-inducing gas.

Q: Do onion tears enter your bloodstream at all?

A: No, the volatile gases only affect the surface of the eyes and do not enter the blood.

Q: Can wearing swimming goggles sufficiently block onion vapors?

A: Yes, swim goggles or other shielded eye protection can effectively stop the gases reaching the eyes.

Q: Will chopping onions a certain way reduce crying?

A: Yes, using a very sharp knife and slicing instead of chopping leaves fewer cell walls ruptured and less gas released.