Are onions poisonous the next day?

In this article, we will answer the question “Are onions poisonous the next day”? and discuss how to store leftover onions?

Are onions poisonous the next day?

No, onions are not poisonous the next day. Cut onions are not poisonous when you handle onions properly. You can store leftover onions in the refrigerator for up to 7 days in a sealed container.

Can leftover onions turn toxic overnight?

Onions do not last forever but they do not go bad overnight. You do not need to throw away the leftovers for fear of them turning toxic. 

Onions are not susceptible to bacterial compounds as onions contain sulfur compounds in them which are repellent to bacteria. Also, onions dry out soon after you cut them, but bacteria grows in moist environments. Bacteria like to grow on high protein content items, and onions don’t contain much protein at all.

Onions may be exposed to bacteria if you cut your onions with a dirty knife or on a dirty cutting board. It does not matter if you stored leftover onions overnight in the fridge, or used them right away, you are vulnerable to getting sick. 

You can use old onions as long as they are not too old. Too old onions can develop mould, which travels through the air. 

Why aren’t cut onions sold?

Cut onions are not readily available despite there being a great demand. This is not because they become poisonous to eat but they deteriorate due to changes in the physical and chemical structure.

Cut onions can be spoiled if onions are not stored in the fridge overnight.

Onions have not responded well to the use of natural food preservatives, so attempts to maximize shelf-life have not worked.

Can I cook old onions?

Yes, you can cook old cut onions if they are just one of many flavouring agents because they are just fine to use.  If the onions are the main flavouring ingredient then it is better to chop onions just before cooking. 

When onions are cut, they release an enzyme called alliinases and this enzyme interacts with amino acids contained in the onions to create a sulfurous, unpleasant odour that can penetrate your dish and disturb flavour. 

How to tell if an onion is bad or spoiled?

There are three ways to tell if your onions have gone bad: colour, feel, and smell. Spoiled onions may develop dark spots, which will eventually begin to grow mould. You’ll also want to avoid onions that have started sprouting, as this indicates they’re beginning to go bad.

You can also feel your onions to check how fresh they are. Onions with soft or mushy spots are starting to go bad.

Other FAQs about Onions which you may be interested in.

Can you eat an onion after it’s been cut?

Are onions a fruit or vegetable?

Are onions and garlic related?

How to store leftover onions?

The frequently asked question is what is the best storage practice to avoid spoilage of cut onions? The answer is to store them in the refrigerator. Once you cut an onion, you need to store any leftover onions in the refrigerator. 

The shelf life of whole peeled onions is 10-14 days in the refrigerator, while diced and sliced onions last for 7-10 days in the refrigerator. It is recommended to store cut onions in a sealed container or plastic bag in the refrigerator.

Even though there are microorganisms inside the refrigerator, due to low metabolic rate at a temperature of 4°C most of them cannot multiply and onion spoilage can be slowed down. But if you had kept the uncut onion at room temperature, it is a good place for fungi to grow.

You can freeze raw onions to extend their shelf-life. Start by peeling the onions, and then chop or slice them as desired. Place them in an airtight container, freezer bag, or wrap them tightly in aluminium foil or plastic wrap. Raw onions will last up to eight months in the freezer.


In this article, we answered the question “Are onions poisonous the next day”? and discussed how to store leftover onions?

Feel free to use those leftovers, raw, pre-cut onions that are sitting in your fridge. Just be sure to always wash your hands, then use a clean cutting board, knife, and storage containers and you’ll be cooking with gas (and be bacteria-free).