why do onions make you cry
The Short AnswerOnions release a chemical irritant called syn-propanethial-S-oxide when their cells are broken. This gas wafts into your eyes and reacts with the water in them, forming a mild sulfuric acid that stings your nerves, triggering tears to wash it away.
The Deep Dive
When you slice or chop an onion, you rupture its cells. This releases enzymes that were previously separated from sulfur-containing compounds called amino acid sulfoxides. These enzymes rapidly convert the sulfoxides into a volatile, unstable compound called syn-propanethial-S-oxide. This chemical is a gas that floats upwards and reaches your eyes. Once in contact with the moisture in your eyes, it reacts with water to form a mild form of sulfuric acid. This acid irritates the nerve endings in your cornea. Your brain interprets this irritation as a threat and signals your lacrimal glands to produce tears. The tears are a protective mechanism, designed to dilute and wash away the irritant, thereby protecting your eyes. Different onion varieties have varying levels of these enzymes and sulfur compounds, which is why some onions are more tear-inducing than others.
Why It Matters
Understanding why onions make us cry helps us appreciate the complex chemistry happening even in simple culinary tasks. It also drives innovation in food science, leading to the development of 'tearless' onions. These are often genetically modified or treated to reduce the production of the irritating compounds, making food preparation more comfortable and accessible for everyone, especially those sensitive to eye irritants. This knowledge also highlights the fascinating defense mechanisms plants employ.
Common Misconceptions
A common misconception is that onions release ammonia, which is what causes the crying. While onions do contain sulfur compounds, ammonia is not the primary irritant. Another myth is that only certain types of onions make you cry. In reality, all onions contain the necessary chemical precursors, but the concentration and specific enzymes vary, making some varieties more potent irritants than others. The 'tearless' onions are a result of scientific intervention to alter this chemical reaction, not a natural immunity.
Fun Facts
- Keeping onions in the refrigerator or freezing them before cutting can reduce the release of the irritating gas.
- Some people are genetically less sensitive to the irritant, crying less or not at all when chopping onions.