You know that burning sensation in your eyes after chopping an onion? And the crying then, just start and after a few minutes comes that uncomfortable feeling. The explanation for this phenomenon is due to the onion cells, part of which is rich in enzymes and the other in sulphides. When cut, these two cells break and mix. A reaction that results in a substance called sulfenic acid and is turned into a gas. Irritation is produced when this gas reaches the eyes.
When the gas comes in contact with water, since the eyes are constantly moist, a weak solution of sulfuric acid is produced. The organism defends itself from the discomfort, producing more tears. A tip to avoid the "crying" is to cut the onions next to a fan, thus avoiding the gases reaching the vision.
Other ways to reduce irritation are: cut onions under running water; cut them into a container filled with water or wash them under running water before cutting.
By Patricia Lopes
Brazil School Team
Source: Brazil School - https://brasilescola.uol.com.br/curiosidades/por-que-cortar-cebola-nos-faz-chorar.htm