Leftover Onion and Cut Onion Q: Are cut onions or leftover onions poisonous? A: When handled properly, cut onions are not poisonous. After being cut, onions can be stored in the refrigerator in a sealed container for up to 7 days. A widely circulated claim states uncooked, leftover onions are ‘poisonous’ because they’re ‘a huge … Continue reading Common Myths