“If you cut me, I won't cry, but I will make your eyes water. What am I?” Almost everyone knows the answer to this riddle: an onion. But why is it that cutting an onion makes our eyes well up with tears? Here is the explanation.
Onions are bulbs that mature underground. They are particularly good at absorbing sulfur, which they use to synthesise several amino acids.
When we cut an onion, we break open numerous cells whose contents come spilling out. It results in the previously separated enzymes meeting the sulfur-rich amino acids and forming unstable sulfenic acids, which then rearrange into a chemical known as syn-propanethial-S-oxide.
The final chemical is a volatile compound, which vaporises, floats up from the chopping board and reaches our eyes, creating a burning sensation. As per Healthline, propanethial S-oxide is a lachrymatory agent, meaning that it generates tears when it touches the eye.
The chemical turns into sulfuric acid when it touches the water layer that covers and protects our eyeballs. To protect the eyes from being damaged, the brain quickly triggers a tear response to rinse the irritant away. This is what causes the red and teary eyes while cutting an onion.
The irritant is part of the onion’s defence mechanism. If a person is allergic or more sensitive to onions, they can display symptoms such as hives, itching and tingling.
While it may sting, the irritants from onions are not actually harmful to the eyes. And not all onions irritate the eyes at the same level. Sweet onions have less sulphur and thus result in fewer tears.
Steps that one can take to reduce irritation and tears include:
Debapriya Bhattacharya is a Content Producer at Hindustan Times. He started his career in 2022, working in newsrooms in beats like education, US news, trending stories, and entertainment. In his new role in the lifestyle desk, he seeks to deliver a balanced blend of research-driven reporting and creative storytelling from health and recipes to art and culture. Science, philosophy, food and pop culture are what pump his veins and help bring heart to his stories. Debapriya tries to see out subjects that will allow him and readers to explore new frontiers and improve the quality of life for all. The explorations can be both external and internal, as thoughts seek to be as chaotic as the greater universe. As a citizen of the world, Debapriya has been fascinated by the lives of people across the globe throughout time. His curiosity leads him to explore new linguistic and cultural landscapes to broaden his horizons and deepen his understanding of global narratives. Beyond the newsroom, Debapriya loves to participate in debate and theatre, spaces that he considers to be holy grounds for nuance and self-expression. A graduate from Ashutosh College, University of Calcutta, Debapriya completed his Master's degree from the same university in 2022. An ambiverted bibliophile, he loves his solitude as much as he adores stimulating conversations. And despite his reverence for tech, libraries continue to be his favourite place for research.Read More
