Why Do Onions Make People Cry?

Onions are a staple ingredient in countless cuisines around the world, known for adding a distinct flavor and aroma to dishes. However, one of the most well - known and often - dreaded aspects of working with onions is the way they make people cry. This phenomenon is not just a random occurrence but is the result of a complex series of chemical reactions that take place when an onion is cut. When an onion is sliced or chopped, the physical act of cutting causes damage to its cells. Onions are made up of millions of cells, each with a specific structure and function. Inside these cells, there are two key components that play a crucial role in the tear - inducing process: enzymes called alliinases and molecules known as sulfoxides. Alliinases are a type of enzyme that are stored in one part of the onion cell, while sulfoxides are located in another. Under normal circumstances, these two substances are kept separate, and no reaction occurs. However, when the cell walls are broken during the cutting process, the alliinases come into contact with the sulfoxides. This interaction is like setting off a chemical chain reaction. The alliinases act on the sulfoxides and start to break them down. Through a series of enzymatic reactions, a volatile compound called syn - propanethial - S - oxide is produced. Volatile compounds are substances that easily turn into a gas at normal temperatures and pressures. This syn - propanethial - S - oxide is no exception; it quickly evaporates into the air around the cut onion.

Once this syn - propanethial - S - oxide gas is released into the air, it can easily reach our eyes. Our eyes are constantly moistened by a thin layer of tears, which helps to keep them lubricated and protected. When the syn - propanethial - S - oxide gas comes into contact with the water in our tears, a chemical reaction occurs. The gas reacts with the water to form sulfuric acid. Sulfuric acid is a well - known irritant, and our eyes are extremely sensitive organs. The human eye has a highly developed sensory system that can detect even the slightest irritants. When the sulfuric acid forms in our eyes, the sensory receptors in the eyes send a signal to the brain. The brain then interprets this signal as a threat to the eyes and activates a protective mechanism. The lacrimal glands, which are responsible for producing tears, are stimulated to produce more tears. This increased tear production is the body's way of trying to wash away the irritant and protect the delicate tissues of the eyes from further damage. It's a natural defense mechanism that has evolved over time to safeguard our visual organs. The intensity of the reaction can vary from person to person. Some people may find themselves quickly reduced to tears after just a few cuts, while others may be able to handle onions with relatively little crying. This difference can be due to a variety of factors, including individual sensitivity to the irritant. Some people may have more sensitive eyes, with a lower threshold for detecting irritants, which means they are more likely to experience a stronger reaction. Interestingly, different onions can cause varying levels of "crying" because the amount of sulfur compounds they contain can differ significantly. The sulfur content in an onion is influenced by several factors, one of the most important being the soil in which the onion is grown. Onions grown in sulfur - rich soil tend to have a higher concentration of these sulfur - containing compounds. For example, in regions where the soil has a high sulfur content, such as some parts of the United States and Europe, the onions grown there are likely to be more potent in terms of their tear - inducing properties. The freshness of the onion also matters. Fresher onions usually have a higher concentration of the necessary enzymes and sulfoxides. As an onion ages, the levels of these substances gradually decrease. This is because the enzymes start to break down over time, and the chemical composition of the onion changes. So, if you pick up a fresh onion from the market, it is more likely to trigger the tear - inducing reaction compared to an older onion that has been sitting in your pantry for a while. Over the years, some people have developed various methods to reduce the impact of onions on their eyes. One common method is to cut onions under running water. When you cut an onion under running water, the water helps to wash away the syn - propanethial - S - oxide gas as it is produced. Since the gas is being constantly removed from the air around the onion, there is less of it available to reach your eyes, reducing the likelihood of the gas reacting with the tears in your eyes to form sulfuric acid. Another popular method is to cut onions in front of a fan. The fan creates a flow of air that helps to disperse the syn - propanethial - S - oxide gas before it reaches the eyes. By blowing the gas away from your face, the fan effectively reduces the concentration of the irritant in the air around your eyes. Some people also try chilling the onions in the refrigerator before cutting them. Cold temperatures can slow down the chemical reactions that produce the syn - propanethial - S - oxide. When the onion is cold, the alliinases are less active, and the breakdown of sulfoxides occurs at a slower rate, resulting in less of the tear - inducing gas being produced. In addition to these practical methods, there have also been scientific efforts to develop "tear - free" onions. Scientists are working on genetically modifying onions to reduce the production of the alliinases or sulfoxides. By altering the genetic makeup of the onion, it may be possible to create varieties that still have the flavor and aroma of traditional onions but without the tear - inducing properties. This could be a game - changer for home cooks and professional chefs alike, making the process of preparing onions a much more pleasant experience. In conclusion, the reason why onions make people cry is a fascinating example of the intersection between biology and chemistry. It shows how a simple act of cutting an onion can set off a complex series of chemical reactions that have a direct impact on our bodies. While the tears may be an inconvenience, they are also a reminder of the amazing protective mechanisms that our bodies have developed to keep our eyes safe. And with the development of new methods and potentially tear - free onions in the future, the days of crying over onions may be numbered.