Why Do Garlic and Onions Make Your Eyes Itch When Cooking?

The sensation of itching, tearing, and watering in your eyes while chopping or sautéing garlic and onions is a common experience for many home cooks. This phenomenon is primarily caused by the release of volatile organic compounds (VOCs) such as allicin from garlic and syn-propanethial-S-oxide from onions. Understanding the science behind these compounds can help you prepare your dishes with less discomfort.

The Chemical Culprits: Volatile Organic Compounds (VOCs)

When you chop or crush garlic, a process known as mechanical damage activates an enzyme called alliinase. This enzyme then catalyzes the breakdown of alliin into allicin, a sulfur-containing compound responsible for garlic's distinct aroma and flavor. Allicin further breaks down or vaporizes into allicin-derived compounds, which can cause irritation in the eyes when inhaled or come into contact with the eyes.

Onions, similarly, contain a compound called syn-propanethial-S-oxide, which is released when the onion cells are broken down. This gas reacts with water in the air and forms fumes that can irritate the eyes. The fumes include sulfuric acid, which is a strong irritant and can lead to the familiar tearing and itching sensation.

Understanding the Chemical Reaction

The compounds released during the chopping process contain sulfur, a common element that contributes to their pungent odor and can cause eye irritation. When these compounds come into contact with the moisture in your eyes, they form sulfuric acid, which can cause a stinging sensation and the associated tearing and itching. The severity of the reaction can vary depending on the intensity and duration of exposure.

How to Minimize Eye Irritation in the Kitchen

While these compounds are an inevitable part of cooking with garlic and onions, there are steps you can take to reduce their impact on your eyes:

1. Chopping Techniques

Use Sharp Knives: Sharp knives are less likely to damage the cells of the garlic and onions, reducing the release of VOCs. Dull knives can cause more mechanical damage, leading to a higher concentration of these irritants.

Chop Under Cold Running Water: Cutting onions under cool running water can help minimize the production of irritants since the water can cool the area and carry away some of the fumes.

Cut From the Root End: Starting from the root end of the onion can help control the release of irritants as you work your way to the top of the onion.

2. Environmental Measures

Keep the Kitchen Ventilation Down: Using a fan or keeping windows open can help dissipate the fumes and reduce the concentration of irritants in the air.

Chill Onions: Letting the onions sit in the refrigerator for 30 minutes before chopping can help reduce the amount of irritant-producing compounds released during the cutting process.

3. Protective Measures

Wear Eye Protection: Wearing goggles or protective glasses can provide a barrier between your eyes and the irritants. Some households even use specialized garlic or onion goggles to keep the irritants out.

Use Garlic Presses: Garlic presses can eliminate the need for chopping, thus reducing the release of irritants. This is ideal for those who are particularly sensitive to eye irritation.

While these measures can significantly reduce the discomfort associated with cooking garlic and onions, it's important to remember that complete elimination of the irritation is not always possible. However, by taking these precautions, you can greatly enhance your cooking experience and maintain a comfortable kitchen environment.

Conclusion

The itching sensation in your eyes while cooking garlic and onions is a result of the chemical reactions involving volatile organic compounds like allicin and syn-propanethial-S-oxide. By understanding these compounds and employing proper chopping techniques, environmental adjustments, and protective measures, you can minimize the irritation and enjoy your cooking session without discomfort.