How to Tell If an Onion Is Bad Onions are a staple in many kitchens, but it can be frustrating to reach for one and find that it has gone bad. Bad onions can ruin a dish, and they can also be a health hazard.
There are several signs that an onion has gone bad. One is if it is soft or mushy. Another is if it has any mold or discoloration. The smell of an onion that has gone bad will also be off, often sour or pungent. If you notice any of these signs, it is best to discard the onion.