Onions have been an ingredient in food - and a cause of bad breath - since the Stone Age, if not before. The pungent plant is a good source of nutrients and vitamins, and many people find it quite tasty. However, the odor molecules packed into an onion bulb can leave anyone who eats it with a powerful case of halitosis.
The earliest known use of onions in cooking stems from at least 5,500 years ago. Onions may have originated in Asia, where cultures prized them for a key characteristic - they do not spoil in the winter, according to Magic Valley Growers.
Today, onions can be eaten raw, grilled, pickled or in a salad or chutney. However, it is difficult to escape one simple fact. Onions cause halitosis.
Maarse's Volatile Compounds in Foods and Beverages says that onions contain hundreds of volatile molecules, many of which contain sulfur. One of the primary odor compounds is 3,4-dimethyl-2,5-dioxo-2,5-dihydrothiophene, which smells similar to hydrogen sulfide, a molecule that gives rotten eggs their aroma.
As if that weren't bad enough, onions also contain the lachrymatory factor, a substance that cause eye irritation and tear production.
To avoid the oral odor and red eyes that onions can cause, individuals who like eating the pungent bulb may consider rinsing with a specialty breath freshener afterward.