Botany expert James Wong explains why chopping onions makes us cry – but not as much as it used to

chopping onions

Onions make our eyes water because of a defence mechanism in the plant which leads to sulphuric acid in your eyes and nose.

While it is certainly an unpleasant experience, the effect is actually far less potent than it once was – because of the rain.

British-Malaysian botanist and broadcaster James Wong has been asked about why chopping onions make people cry so often he decided to answer the question publicly.

He wrote a comprehensive thread on his Twitter account which put the issue to rest.

He said: “When you cut into an onion the ruptured cells deploy an airborne, sulphur-based chemical into the room.

“When it mixes with the water in your eyes & nose it turns into sulphuric acid. A chemical defence created by plants.”

Interestingly, as well as repelling us from cutting into the onion, the process could also prove to be very useful in treating ailments.

Wong continued: “This chemical not only repels mammals who might be attempting to munch on the bulbs, but is also toxic to bacteria and fungi, helping prevent infection at the site of the wound.

“As humans we can hijack this chemical & use it to treat microbial infections on our bodies too!”

The chemicals released are even harmful to the onion and are only created in desperate times – such as someone chopping into the bulb with a sharp knife.

Wong said: “This compound is so potent however it is even toxic to the plant itself.

“So intact onions don’t contain any at all. It is only created at the site of cellular damage when 2 separate chemicals come into contact with each other. Like a 90s glow stick.”

Because of changes in the rain in the UK, the chemicals released by onions are not as strong as they have been in the past.

Wong added: “The weirdest thing?

“Onions get the sulphur to make these compounds from the soil they grow in. An important part of the sulphur in U.K. soils came from the sulphuric acid in acid rain. No, really.

“So our onions are getting less pungent (& maybe less nutritious) over the years.