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Cutting onions can cause burning eyes and intense watering, especially when working with particularly pungent varieties or large quantities. This is completely natural: when the blade breaks the onion's cells, certain sulfur-containing substances come into contact with specific enzymes and produce an irritating volatile compound.

This compound reaches the eyes through the air and stimulates tear production, which the body uses to dilute and ward off. Working directly under running water can partially reduce its diffusion, but it's neither the most practical nor the safest method. The cutting board may move, your grip on the knife may become less stable, and the water may disperse some of the onion's aroma.

There are simpler and more effective measures, such as cooling the vegetable, using a very sharp blade and improving kitchen ventilation.

Why does onion make you cry?

Onions keep different substances separate within them. When cut, crushed, or chopped, the cells break and their contents mix.

This reaction produces a volatile substance that disperses into the air. When it reaches the moist surface of the eyes, it causes irritation and stimulates the tear glands. The more cells are damaged, the greater the amount released.

For this reason, a dull blade, which crushes the flesh instead of cutting it cleanly, tends to cause more tears than a sharp knife. Even chopping onions finely generally produces more irritants than dicing them into a few large pieces.

Cool the onion before cutting

One of the simplest methods is to place the onion in the refrigerator for about 20-30 minutes before using it. The low temperature slows the reactions that produce volatile compounds and temporarily limits their diffusion.

It's not necessary to regularly store them in the refrigerator. Whole onions generally prefer a cool, dry, dark, and ventilated place. Refrigeration is recommended only shortly before cooking.

The freezer must be used with greater caution. A few minutes can quickly cool onions, but too long a stay can alter their texture and make them more difficult to slice evenly.

Use a very sharp knife

A sharp blade cuts through the layers with a clean cut and breaks fewer cells than a knife that must be pressed and dragged repeatedly.

Before starting, it's therefore important to choose a suitable, stable, and sufficiently long knife. The cutting board must also be firm. To prevent it from slipping, you can place a slightly damp and well-wrung-out cloth underneath.

The onion should rest on the flat side obtained after the first cut. This position offers greater stability and reduces the risk of it rolling while slicing.

Working with regular movements and without crushing the pulp helps limit the release of irritating aromas and makes the cut more precise.

Leave the root until the end

The root end can be left attached for most of the preparation process. Besides holding the layers together, it helps you handle the onion while slicing or dicing.

It's incorrect to think that all the substances responsible for tears are concentrated exclusively in the root. Leaving it intact, however, prevents immediate breakage of an additional part of the bulb and facilitates a more orderly work process.

You can first remove the top, cut the onion in half, peel it, and continue cutting, keeping the root as a support. Only at the end should you remove the last portion.

Improve ventilation

Opening a window, turning on the extractor hood, or working near a draft can blow volatile substances away before they reach your eyes.

A small fan can be placed to the side, orienting it so that it blows air from the cutting board area toward a window or away from the face. It should not be directed at the eyes, as this could increase dryness and discomfort.

Body position also matters. Keeping your face too close to the cutting board increases exposure to fumes. It's best to maintain an upright posture and a comfortable distance, without sacrificing control of the knife.

Is it useful to cut onions under water?

Water can capture and dilute some of the irritants, but chopping onions directly under the tap has several drawbacks.

The surface can become slippery, the cutting board can lose stability, and it becomes more difficult to control the blade. Furthermore, running water produces unnecessary waste and can remove some of the aromatic compounds responsible for flavor.

A less problematic alternative is to quickly rinse the peeled onion with cold water and dry it before cutting. The anti-tearing effect is limited, but the procedure does not compromise safety on the work surface.

Cutting onions while immersed in a bowl of water is even less practical and increases the risk of accidents. It's therefore better to rely on cold, well-ventilated areas and a sharp blade.

Can glasses help?

Eyeglasses offer only partial protection, as air can enter the eyes from the sides. Well-fitting protective goggles or simple swimming masks, however, prevent vapors from directly contacting the ocular surface.

It may seem like an unusual solution, but it is particularly effective when you have to slice a lot of onions, for example when preparing preserves, soups or large quantities of soffritto.

Contact lenses may reduce the perception of irritation in some people, but they should not be considered a protective measure. It's always important to handle them with clean hands and avoid touching your eyes after processing onions.

Unreliable traditional remedies

Holding water, bread, or a spoon in your mouth doesn't reliably prevent volatile compounds from reaching your eyes. Even breathing through your mouth alone offers limited benefit, because the irritant spreads through the air regardless of how you breathe.

Lighting a candle near the cutting board is sometimes recommended, but the effect is inconsistent and introduces an open flame near hands, utensils, and flammable materials.

It is best to use methods that actually improve working conditions, without additional distractions or risks.

What to do when your eyes burn

If the tearing becomes intense, put down the knife, move away from the cutting board, and go to a well-ventilated area. It's not advisable to rub your eyes, especially with hands that have just touched the onion.

Hands should be washed thoroughly with soap and water. If necessary, eyes can be gently rinsed with clean water. The discomfort usually subsides quickly.

Very strong, persistent, or painful irritation requires greater attention, especially if onion juice, fragments, or other products have entered the eyes.

In conclusion

To reduce tears while chopping onions, it's best to cool them briefly, use a sharp knife, and work in a well-ventilated area. Leaving the root until the end and keeping your face away from the cutting board helps keep the process tidier.

Cutting under running water can reduce some of the fumes, but it makes the work surface slippery and isn't the safest solution. With proper preparation and the right tools, you can significantly reduce the discomfort without compromising the flavor of the onion.

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