Onions come in many different shapes and sizes, the most common of which are yellow onion, red onion, garlic and chives. The picture on the right shows a leek, which is also a kind of onion.

Onions have a strong smell, which is caused by substances contained in their cells. Some onions can even make you cry when you are cooking with them. The crying reflex is triggered when the onion's aromatic substances are released into the air.

Onions are a good source of vitamins and nutrients.