Our favourite Pao Bhaji or even the Bhel Puri would be so incomplete without being garnished with freshly cut pink shallots. Our Indian curries would be tasteless without onion pastes; our pulses would taste bland without a topping of the ‘tadka’ with stir-fried brown onions. But, a lot of effort and pain goes into making any of these delicious flavours – in the case of onions - they make us weep. As Shakespeare put it in his play All’s Well That Ends Well – ‘Mine eyes smell onions; I shall weep anon’.

In addition to flavouring many dishes, onions are also prepared pickled, boiled, sautéed, and deep-fried. Besides fresh onions, onions are also available as canned, frozen, and dehydrated as a spice or powdered.

The word ‘onion’ comes from the Latin word unio meaning ‘single’, or ‘one’, since onions grow as a single bulb, unlike its cousin, the garlic, that produces many small bulbs. The name also describes the union (unio) of the many separate layers of the onion.

There are many different varieties of onion, mostly recognized by their colour – red, yellow, white, and green, each with their own unique flavour, from very strong to slightly sweet. Mainly onions are divided into two categories – green and dry. Green onions are the ones harvested while their shoots are still young and green. Dry onions can be red, white, or yellow in colour. They are harvested once the shoots have died and the onions are left with a paper-like covering encasing the fleshy vegetable. Yellow storage onions are available throughout the year but the sweeter varieties have a more limited growing season and are available only a few months in a year.

Onions (Allium cepa) belong to the lily family, with garlic, leeks, chives, scallions and shallots as its relatives. There are over six hundred species of Allium, found all over Europe, North America, Northern Africa and Asia. There are over a hundred and twenty recognized uses of the Alliums.

Onions have a variety of medicinal effects. Early American settlers used wild onions to treat colds, coughs, and asthma, and also insect repellants. In Chinese medicine, onions have been used to treat angina, coughs, bacterial infections, and breathing problems.

The Alliums have a rich content of thiosulfinates, sulfides, sulfoxides, and other odoriferous sulfur compounds. The cysteine sulfoxides are primarily responsible for the onion flavour and producing of eye-irritating substances that induce watering of the eyes. The thiosulfinates show anti microbial properties. Onion is effective against many bacteria including Bacillus subtilis, Salmonella, and E. coli. In this case, garlic is more potent than onions due to the presence of a higher content of sulfur compounds.

The World Health Organization (WHO) recognizes the use of onions for the treatment of poor appetite and to prevent atherosclerosis. In addition, they also support that onion extracts are being used to provide relief in the treatment of coughs and colds, asthma and bronchitis; onions are known to decrease bronchial spasms. An onion extract was found to decrease allergy-induced bronchial constriction and improve lung function in asthma patients.

Onions are a very rich source of fructo-oligosaccharides. They stimulate the growth of healthy bifidobacteria and reduce the growth of harmful bacteria in the colon. Also, this can reduce the risk of developing tumors in the colon.

Onions contain a number of sulfides similar to those found in garlic, which may lower blood lipids and blood pressure. In India, communities that do not eat onions or garlic had blood cholesterol and triglyceride levels substantially higher, and shorter blood clotting times, than the communities that consumed moderate amounts of garlic and onions.

Onions are a rich source of flavonoids, substances known to provide protection against cardiovascular diseases. Onions are natural anti clotting agents since they possess substances with fibrinolytic activity and can suppress platelet clumping – they diminish the risk of blood clots. The anti clotting effect of onions is also correlated with their sulfur content.

Onion extracts, rich in a variety of sulfides, provide some protection against tumor growth, including one in stomach cancer, ovarian cancer, breast cancer, renal cell cancer, prostrate cancer and others. Chinese, who have the highest intake of onions, garlic, and other Allium vegetables, have a risk of stomach cancer forty percent less than those with the lowest intake.

Many despise freshly cut raw onions, for the bad breath that follows. Hence, people tend to buy the less pungent, milder onion varieties. This may not be the best choice, since the onions with a stronger flavour and higher astringency appear to have superior health-promoting properties. The more pungent varieties of onion appear to possess the greatest concentration of health-promoting phytochemicals.

Onions are universally accepted and used for flavouring in most communities. However, consuming large quantities of onions can lead to stomach distress and gastrointestinal irritation that may result in nausea and diarrhea. There are no known reactions of onions with drugs except that they can trigger the action of anticoagulants.

When selecting fresh onions in a store, one should look for firm and dry onions with a shiny, crackling outer skin. Onions with excessively strong odours might be an indication of rotting. Fresh whole onions should have a mild odour. Onions with dark spots should also be avoided as this can indicate mould. Sweet onions should be used fresh because they perish soon. To get the best flavour out of sweet onions, they should be bought and used within a day or two.