16 Fascinating Facts About the Humble Onion

facts about onions

Onions are one of the most widely used vegetables in cuisines around the world. Their versatility, flavor, and health benefits make them a staple in many kitchens. But beyond their culinary uses, onions have a long and fascinating history.

Here are 16 interesting facts you may not have known about this humble bulb:

1. Onions are ancient – dating back over 5,000 years

Onions have been cultivated for millennia. They are native to central Asia and were likely first grown in modern-day Iran and Pakistan.

There is evidence that onions were grown in Chinese gardens as early as 5,000 years ago. Ancient Egyptians revered the onion and used it as currency to pay workers who built the pyramids and placed them in the tombs of kings.

Onions were brought to North America by the first European settlers and Native Americans were already cultivating wild onions when colonists arrived.

2. Onions belong to the Allium family

Onions belong to the Allium family of vegetables along with garlic, shallots, leeks, scallions, and chives. Allium vegetables contain beneficial organosulfur compounds which are responsible for their pungent aromas and many of their health benefits.

3. There are many

varieties of onions
varieties of onions

While yellow onions are most common, there are actually hundreds of cultivated varieties.

  • Red onions have a mild sweet flavor when raw and are often used in salads, sandwiches, and as a colorful garnish.
  • White onions are the mildest in flavor and don’t overpower other ingredients. They are perfect for Mexican and Italian dishes.
  • Shallots have a delicate, sweet onion flavor. They grow in clusters somewhat like garlic and have brown papery skin.
  • Pearl onions are small, bite-sized onions used in stews and gravies.
  • Scallions (green onions) are actually immature onions, harvested before the bulb fully forms. Both the long green stalks and small white bulbs are edible.
  • Cipollini onions are small, flat onions with a sweet and mild taste.

4. Onions make you cry for a good reason

handsome young man crying while cutting onion
handsome young man crying while cutting onion

Cutting an onion releases a gas that wafts into your eyes and causes them to water. This gas is actually a defense mechanism to deter pests.

Onions produce a gas called syn-propanethial-S-oxide when their cells are damaged. The gas mixes with the natural moisture in your eyes to form sulfuric acid, which irritates the eyes.

5. You can stop onion tears with proper cutting technique

Cook cutting onion in professional way
Cook cutting onion in professional way

To prevent crying while cutting onions, use a super-sharp knife to damage fewer cells. Chilling the onion for 30 minutes before cutting also reduces the gas released.

Cutting under running water or wearing goggles are other options, although not very practical!

6. Onions provide several important nutrients

Despite their small size, onions are packed with nutrients. Some of the key nutrients found in onions include:

Nutrition FactsAmount per Portion% Daily Value*
Portion Size100 gN/A
Total Fat0.1g0%
Total Carbohydrate9.3g3%
Dietary Fiber1.7g6%
Vitamin D0mcg0%

* The % Daily Value (DV) tells you how much a nutrient in a serving of food contributes to a daily diet. 2000 calories a day is used for general nutrition advice.

  • Vitamin C – An antioxidant that supports immune function.
  • Folate – Important for cell growth and prevention of birth defects.
  • Vitamin B6 – Plays a role in immune function and energy metabolism.
  • Potassium – A mineral and electrolyte that regulates fluid balance.
  • Fiber – Improves digestion and heart health.

7. Onions contain powerful health-promoting compounds

Onions get their sharp flavor from sulfur-containing compounds. Two classes of these are thiosulfinates and thiosulfonates.

In addition to giving onions their pungent kick, these compounds have antioxidant, anti-inflammatory, anticancer, and antimicrobial effects in the body. Quercetin is another beneficial plant compound found in onions.

8. Onions may boost heart health

Several studies have linked increased onion consumption to lower heart disease risk. Their anti-inflammatory and sulfur compounds are believed to reduce high blood pressure and cholesterol levels.

A review of 8 studies found that higher allium vegetable intake was associated with a 15% lower risk of heart disease and stroke. More research is needed to confirm direct cause and effect.

9. Onions may help control blood sugar

Onions contain allyl propyl disulfide which has been shown to lower blood sugar levels by increasing insulin production. They also rank low on the glycemic index, meaning they won’t cause major spikes in blood sugar.

A study in diabetics found that consuming 3.5 ounces of fresh red onion decreased fasting blood sugar levels by about 40 mg/dl after 4 hours. More research is needed in non-diabetics.

10. Onions are antibacterial and antiviral

Lab studies have found onion extract to be effective against various bacteria including E. coli, Bacillus cereus, and Salmonella. The antibacterial effects are thought to come from their sulfur compounds.

Onions also have antiviral properties. Quercetin extracts from onions have been shown to inhibit viral infection and replication.

11. Onions can boost digestive health

The high fiber content of onions promotes good digestion and gut health. The prebiotic fibers in onions act as food for beneficial gut bacteria.

They may help increase the number of bifidobacteria which are linked to reduced inflammation, cancer prevention, and other health benefits.

12. Onions can help build strong bones


Onions contain gamma-glutamyl peptides that appear to stimulate osteoclast cells responsible for bone resorption. Adequate intake of vitamin C and other bone-supporting nutrients in onions also promote bone health.

A study in menopausal women found that daily consumption of onions reduced markers of bone loss. More research is needed to confirm direct effects on bone mineral density.

13. Onions have been used for centuries in folk medicine

For centuries before modern medicine, cultures around the world used onions for their therapeutic properties.

  • Hippocrates prescribed onions as a diuretic, wound healer, and digestive aid.
  • Ancient Greek Olympians ate onions to enhance performance.
  • In the Middle Ages, onions were believed to repel witchcraft and evil spirits.
  • During plague outbreaks, people ate onions to protect against infection.

14. Onions can be used to dye Easter eggs

The outer skin of yellow and red onions contains a water-soluble pigment that can be used to dye Easter eggs.

Simply boil peeled onion skins in water and let cool. Dip hard boiled eggs into the onion dye water and let sit for 10 minutes before removing. The eggs will take on a beige, orange, or reddish hue.

15. Egyptians worshipped the onion

egypt onion
image created by AI

Ancient Egyptians revered the onion and used it as currency. Paintings of onions appear on the inner walls of several pyramids and onion bulbs were found in the eye sockets of Ramesses IV.

Small onions were also placed in the abdominal cavities of mummies to nourish kings in the afterlife. Egyptians took oaths with onions instead of the Bible.

16. You can determine an onion’s age by its rings

When you cut an onion in half horizontally, you’ll see a series of concentric rings in the flesh. Each ring represents a cycle of growth and dormancy. New rings form as the onion matures.

Wide rings indicate favorable growing conditions while narrow rings suggest the onion struggled to grow. The number of rings can determine the onion’s age and harvest season.

So there you have it – a few fun facts you may not have known about the humble, yet mighty onion. This versatile vegetable has a long history of use around the world and remains an essential ingredient in many cuisines.

Onions provide a unique flavor and nutrition boost to recipes while also offering some impressive health benefits. Next time you’re chopping onions for dinner, appreciate this fascinating allium!


When you cut into an onion, it releases a gas called syn-propanethial-S-oxide. This gas reacts with the moisture in your eyes to form sulfuric acid, which irritates your eyes and causes them to water.

  • Use a very sharp knife to damage fewer onion cells that release the irritating gas.
  • Chill the onion in the fridge for 30 minutes before cutting to reduce the amount of gas released.
  • Cut under running water to wash away the gas before it reaches your eyes.
  • Wear goggles or safety glasses to create a barrier between your eyes and the gas.

Onions contain powerful antioxidants like quercetin and sulfur compounds that may help reduce inflammation, lower cholesterol, regulate blood sugar, fight bacteria and viruses, and promote bone health.

Common varieties include yellow, white, red, pearl, cipollini, shallots, scallions, and sweet onions like Vidalia. Each has a slightly different taste, texture, and color.

Store whole, dry bulbs in a cool, dark, well-ventilated place. Do not refrigerate them. Once cut, onions should be tightly wrapped and refrigerated for no more than 7 days.

Yes, onion skins are edible and full of fiber and antioxidants. The papery outer layers can be eaten, though the thicker inner layers are sometimes removed for texture. Leaving skins on adds nutritional value to dishes.

Whole, uncut onions can last 1-2 months at room temperature. Once cut, onions will last about 7-10 days tightly wrapped in the refrigerator. Cooked onions last 3-4 days in the fridge.

No, onions are toxic to dogs and cats. Onions contain compounds that can damage their red blood cells and cause anemia when ingested, even in small amounts. Keep onions away from pets.

Yes, raw onions are safe to eat and provide the most nutritional benefits. Be sure to rinse them under water first to remove any dirt. Those with sensitive stomachs may experience gas or bloating from raw onions.

Scallions and green onions come from the same onion species, but scallions are harvested earlier before the bulb fully forms. So scallions have a long green stalk with a small white portion.

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