Onions pickled in vinegar are eaten as a snack. These are often served as a side serving in fish and chip shops throughout Australia, often served with cheese in the United Kingdom and are referred to simply as "pickled onions" in Eastern Europe. Onions are widely used in Iran and India and Pakistan, and are essential to daily life in the local cuisine. They are commonly used as a base for curries or made into a paste and eaten as a main course or as a side dish.
Onions are also used as an aromatic in cooking. In the classic mirepoix it is used along with celery and carrots to flavor stocks, soups, stews and sauces.
Onions have particularly large cells that are readily observed at low magnification; consequently, onion tissue is frequently used in science education for demonstrating microscope usage.
3-mercapto-2-methylpentan-1-ol in onion was found to have an antioxidant potent that inhibits peroxynitrite induced diseases.
The amount of sulfenic acids and LF released, and the irritation effect, differs among Allium species. On January 31, 2008, the New Zealand Crop and Food institute created a strain of "no tears" onions by using gene-silencing biotechnology to prevent synthesis by the onions of the lachrymatory factor synthase enzyme.