Why do onions make you cry?
They’re a staple ingredient of many recipe favourites but why do onions make you cry?
Although the unpleasant sensation may be familiar, onion tears are not the same as crying in the emotional sense of the word, perhaps as you would at a sad romantic movie. These impulsive tears are called ‘psychic tears’ which occur when a stimulus evokes an emotional reaction. Onion tears, however, belong to the category of ‘reflex tears’. ‘Reflex tears’ occur when an external stimulus acts upon the lachrymal gland which regulates tear production. When onions grow in the ground, they absorb sulphur from the soil. This sulphur forms a sulphur compound (sulphide), which is converted to enzymes called syn-propanethial S-oxide. It’s these enzymes which act as the stimulus affecting our eyes.
When an onion is cut, the cells are damaged and these enzymes, called ‘allinases’, are released as a gas, causing the familiar unpleasant stinging sensation and tears.
Your body’s natural reaction is to try to expel or dilute the onion irritant from the eye with tears, so when the brain registers an irritation, the lachrymal gland is stimulated to produce tears.
There are various steps you can experiment with to minimise the effect of these unpleasant gases reaching your eyes:
1. Keep your onions in the fridge
Chilling onions for half an hour or so before preparation is believed to slow the movement of the sulphuric vapours, thus reducing their irritating effect on your eyes.
2. Cut with a sharp knife
A sharp knife requires less pressure to cut through the onion and less pressure means less cell damage. Fast, precise slicing also minimises time spent chopping the onion and releasing the gases.
3. Avoid the root
The root is thought to contain the highest concentration of the syn-propanethial S-oxide gas. Try avoiding cutting through the root to prevent the irritants from escaping into the air.
4. Wear goggles
It may seem extreme and may look odd but onion goggles can prevent eye irritation by protecting your eyes from the unpleasant gases.
But although they make you cry, the sulphur in onions has benefits for the eyes in helping to reduce the risk of cataracts. Similarly, onions (particularly red) contain quercetin, a potent antioxidant thought to help prevent cataracts. Antioxidants are compounds which can help to delay or slow the oxidative damage to tissue and cells in the body. Most of these precious antioxidants can be found in the outer layers of the onion’s skin so, during preparation, avoid removing too many of the edible layers.
Victoria writes for DirectSight, supplier of cheap glasses online .