A few months ago, I heard Dr Oz say that once you cut an onion, it should be secured in a proper container before refrigeration. He stated that a loose cut onion, would absorb bacteria from other foods in the refrigerator. I had been noticing, that onions lost their flavor once cut and refrigerated for a few days, if they were not in a secure container.
I assumed, based on what Doctor Oz said, that the onions were obtaining bacteria and the scent from other refrigerated foods. I began to make sure onions were in zip lock bags or plastic containers with air tight lids. Recently my husband told me that he heard that once you cut an onion, it has to be eaten right way, because left over onion emits poisonous gas that can cause illness.
I have been eating leftover onions for most of my life without a problem. I also did not see myself throwing away a perfectly good onion, after cutting a few slices for a salad or burger.I did some digging and here is what I believe to be the most accurate information regarding cut onions.
They are safe to use, provided they are stored in proper containers and good hygiene is used. Please wash your hands and the onion. Wash hands again after cooking or storing onions. Truthfully, most of us have eaten onions that have sat out all day during a picnic, or on the counter of a lunch buffet. I have never heard of anyone getting sick.
I did listen to my grandmother and mother in law tell stories of people in the old days, who put onions in their socks and were healed of severe cold or flu. My grandmother often ate raw onion and said it helped her stay healthy.
According to Livestrong.com, cut onion is good for up to two weeks in a pantry, and two months in a refrigerator. They recommend washing hands, knives, cutting boards and everything that comes in contact with the onion, to prevent transference of bacteria.