Do you know why onions make us cry?

Do you love cooking, but prefer to skip your turn when it comes to cutting onions? Nothing could be more normal... Because as delicious as they can be, onions have an unfortunate tendency to make us cry. How to explain this phenomenon ? And above all, how to avoid it? We take stock.

Fans of pissaladière, onion soup or even ratatouille know this well… Onions sting the eyes  ! But where exactly does this property come from? And what are the best techniques for peeling and cutting a fresh onion without shedding a tear on the cutting board?

Onions make you cry: a question of chemistry!

Like shallots, onions can indeed make us cry... As Dr Jean du Breuillac, general practitioner and deputy secretary general of the College of General Medicine (CMG), explains to us, it is a completely chemical reaction. completely natural and almost inevitable .

Propanesulfonic acid, a merciless irritant…

Onions contain many sulfur compounds . When cut, aliinase enzymes are released which mix with sulfur compounds to better form sulfenic acid. Too unstable, the latter spontaneously reorganizes into propanethial oxide (syn-propanethial-S-oxide), a tear gas which disperses in the ambient air and generally ends up reaching our cornea.

This is where things get tricky. As Dr du Breuillac reminds us, our cornea is constantly hydrated by basal tears which aim to oxygenate it but also to lubricate and nourish the cells of the eye. However, at the slightest contact with humidity, propanethial oxide transforms into  propanesulfonic acid , a liquid as irritating as sulfuric acid: hence the intense burning sensation in the eyes!

In this case, our tear glands activate and begin to produce as many tears as possible to protect our eyes and quickly eliminate the irritating acid. Concretely, these so-called “reflex” tears allow us to rinse our eyes and reduce unwanted symptoms. Dr Jean du Breuillac, general practitioner.

Good to know: this chemical reaction is a natural adaptation of the onion to protect itself from predators and pathogens. In practice, these sulfur compounds prevent infections and help extend the life of onions by inhibiting the growth of bacteria and fungi. That said, they  no longer take effect when the onions are cooked  !

Eye health: is onion good for eyes?

As you probably know, it is absolutely not recommended to eat onions. Given their richness in antioxidants , their consumption is rather encouraged as part of a varied and balanced diet.

Contrary to what you might think, onions are not dangerous for our eye health. The tearing is temporary and the irritation subsides as soon as exposure stops . That said, it may last longer if onion juice comes directly into contact with your eyes...

How to avoid crying while peeling or cutting an onion?

Although it is impossible to completely eliminate the irritant effect , certain tips help limit the production of tears...

Peel an onion without crying

In theory, peeling onions poses few risks. But we are never safe from a bad surprise! To avoid tears , you can:

  • peel the onion under water;
  • peel the onion as quickly as possible;
  • peel the onion under an extractor hood;
  • direct a fan towards your work surface;
  • or refrigerate the onion for at least 30 minutes before peeling.

Cutting an onion safely

  • Before cutting, place the onion in the refrigerator for 30 minutes (or in the freezer for about 15 minutes).
  • Use a sharp knife which will break the onion cells less and reduce gas formation.
  • Cut the onion under a stream of cold water  or install a water source near your work surface.
  • Stick your tongue out for the duration of the cut , so your saliva will capture the irritating gas and your eyes will be spared. Some people even recommend chewing gum to increase saliva production!
  • Cook in a well-ventilated space to help disperse the irritating gas (open your windows or use an extractor hood).
  • Wear protective goggles , ideally sealed swimming goggles, to prevent irritating vapors from coming into contact with your eyes.

Everyone has their own method! In any case, once the onion is cut, remember to wash your hands well , or even rinse them with lemon juice or vinegar before running them under cold water.

“Sunions”, finally a variety that doesn’t sting the eyes!

Can't bear to shed a tear every time you cut an onion? At the risk of surprising you, there is a revolutionary variety of onions: sunions . Although they are identical in every way to traditional yellow onions, they still have the particularity of not making us cry. FYI, these onions are not the result of genetic manipulation but of natural crossing! “It took thirty years of research in conventional breeding to develop this onion,” explains David Corré, head of the seeds sector at BASF France, recently interviewed by 20 minutes (source 1).