Why Onions Make You Cry

It’s a familiar kitchen scene: you start chopping an onion, and before you know it, your eyes are watering like you’ve just watched a sad movie. But why do onions have this tear-inducing power? It turns out that there’s some fascinating science behind those onion tears. Let’s dive into the chemistry of why onions make us cry and explore if there’s anything you can do to keep your eyes dry.

The Chemistry Behind the Tears

The culprit behind onion-induced crying is a chemical reaction that takes place when you slice into an onion. When an onion is cut, its cells are damaged, releasing an enzyme called alliinase and a sulfur-containing compound known as sulfenic acid. The enzyme reacts with the sulfenic acid, converting it into syn-Propanethial-S-oxide, a volatile compound.

Syn-Propanethial-S-oxide is a type of lachrymatory agent, which means it stimulates the lachrymal glands in your eyes, causing them to produce tears. When this compound becomes airborne, it reaches your eyes and reacts with the moisture on the surface, forming a mild sulfuric acid. This acid irritates the nerve endings in your eyes, leading to the familiar burning sensation and triggering a reflex to produce tears to wash away the irritant.

Why Are Some Onions Worse Than Others?

Not all onions are created equal when it comes to making you cry. The strength of the tear-inducing effect depends on the variety of onion, how it’s grown, and even its freshness. Here are some factors that influence the severity of your onion tears:

• Onion Type: Yellow, white, and red onions tend to be more pungent and have higher concentrations of sulfur compounds, making them more likely to cause tears. In contrast, sweeter onions like Vidalia or green onions have lower sulfur levels and are less irritating.
• Growing Conditions: The amount of sulfur present in the soil where the onion was grown can also affect its pungency. Onions grown in sulfur-rich soil tend to produce more sulfur compounds, leading to more tears.
• Storage and Freshness: Older onions can actually produce stronger tear-inducing chemicals because they may lose some of their natural sugars over time, which help balance out the sulfur compounds.

Are Tears the Onion’s Defense Mechanism?

Interestingly, the ability of onions to make you cry is thought to be an evolutionary defense mechanism. The compounds that are released when an onion is cut serve to deter animals, insects, and even some microorganisms from eating the onion or damaging its cells. It’s a bit like the onion’s way of saying, “Don’t eat me!”

How to Minimize Onion Tears

While you can’t eliminate onion tears entirely, there are some tricks to reduce their severity:

1. Chill the Onion: Placing the onion in the refrigerator for 30 minutes before chopping slows down the chemical reaction that releases the tear-inducing compounds.
2. Use a Sharp Knife: A sharp knife causes less cell damage, releasing fewer irritants.
3. Cut Near a Vent or Fan: Position yourself near a fan or vent to blow the onion fumes away from your face.
4. Cut Under Running Water: Cutting the onion under running water or submerging it in water can help dissolve some of the sulfur compounds before they reach your eyes.
5. Wear Goggles: While it might look a bit silly, wearing protective goggles can create a barrier between your eyes and the onion’s fumes.

The Onion-Eye Connection: More Than Just Tears?

Interestingly, onions don’t just make you cry—they can also affect the way you perceive their taste. When your eyes water, your nose might run as well, affecting your sense of smell. Since taste and smell are closely linked, this can alter your overall perception of the onion’s flavor. The combination of tearing and nasal irritation is all part of the complex experience of cutting an onion.

Why Don’t We Cry When We Eat Cooked Onions?

If you’ve ever wondered why cooked onions don’t make you cry, it’s because the cooking process inactivates the enzymes responsible for producing the tear-inducing compounds. Heat denatures the enzyme alliinase, preventing it from reacting with the sulfur compounds to form syn-Propanethial-S-oxide. As a result, cooked onions are tear-free and much milder in flavor.

Are Onions the Only Vegetables That Make You Cry?

Onions belong to the Allium family, which includes garlic, shallots, leeks, and chives. Many members of this family contain sulfur compounds, but onions are unique in having high levels of syn-Propanethial-S-oxide, making them particularly potent tear-producers. Garlic and other Allium vegetables may produce a milder version of the effect, but it’s usually not enough to make your eyes water.