Cooks use them almost everyday and they are one of the most versatile ingredients in the kitchen.
But if you've been keeping your onions in the fridge instead of the cupboard, then you've been storing them wrong, reports the Daily Mail.
Now it has been revealed exactly what happens to the vegetable when they are kept at too cool a temperature - and it will cause them to go off very quickly.
The United States Department of Agriculture (USDA) has reported that when an onion is chilled, the sugars in the vegetable convert to starch.
This causes the onion to go soggy, soft and ultimately inedible - not to mention they will give off a foul odour that will soon seep into every item in your fridge.
But if you keep onions in a cool, dark place, they can last for up to 30 days, Good Housekeeping says.
However, you shouldn't keep them in a brown paper bag, despite many people believing this is the best way to store them.
Onions need space and air to breathe to stop them from sprouting and from going off too quickly.
So the best way to store them is to keep them in a cool, dark place, preferably in a kitchen cupboard.
You can also keep them in a bowl on the kitchen table in their original mesh, if you prefer.
The best temperature to store onions at is a cool 7C - certainly colder than most kitchens.
So if you're lucky enough to have a basement or cellar, it may be best to keep your onions underground.
Just whatever you do, keep them away from your potatoes.
"Don't keep them in the same place as your potatoes, or you'll find your spuds are sprouting faster," revealed Good Housekeeping consumer editor Sara Benwell.