Why Do Onions Hurt Some People’s Eyes More Than Others?

Everyone has experienced the uncomfortable feeling of having their eyes watering and burning while chopping onions. However, the intensity of this experience can vary significantly from person to person. This variation is due to a combination of chemical composition, genetic factors, eye health, technique, preparation, and environmental conditions.

Chemical Composition

Onions release a gas called propanethial S-oxide when they are cut. This gas reacts with the moisture in the eyes, forming sulfuric acid, which leads to the burning sensation and tearing. Some individuals are more sensitive to this compound than others, making their eyes more vulnerable to the irritating effects of the gas.

Genetic Factors

Genetic differences can also play a role in how much irritation individuals experience. Genetic variations can affect the density of nerve endings and how sensitive they are to irritants. People with heightened sensitivity to pain and irritation may experience more discomfort when chopping onions.

Eye Health

Pre-existing eye conditions such as dry eyes or allergies can exacerbate the discomfort experienced when chopping onions. Individuals with dry eyes may find the conditions during the process more troublesome.

Technique and Preparation

The way onions are cut can also impact the amount of irritating gas released. For example, slicing an onion versus chopping it can release different amounts of irritants. Using sharper knives or specific cutting techniques can reduce the gas release and subsequent irritation.

Environmental Factors

The environment in which onions are cut, such as ventilation and humidity, can affect how much of the gas is dispersed and how much reaches the eyes. Optimal ventilation can help mitigate the irritants in the air.

A Comprehensive Factor

Overall sensitivity to onion-induced eye irritation is a combination of biological, genetic, and environmental factors. This explains why different individuals experience varying levels of discomfort while handling onions.

Additional Info about Onions

Onions are not only pungent but can also influence body odor. Eating onions can subtly change the smell of your sweat, and this is more noticeable if you engage in activities that produce significant sweat, such as exercise or heavy labor. However, some individuals are not bothered by this phenomenon, but it is a common observation.

Beyond the Eyes: Fructans and Digestive Issues

Fructans, a type of carbohydrate found in onions, are a group of short-chain sugars that cannot be absorbed in the small intestine. Humans do not produce the enzymes needed to break the bonds between these sugars. As a result, fructans move through the gut unabsorbed and reach the large intestine, where they are fermented by bacteria. Many people experience bloating and gas after eating onions. Those with a sensitive gut may experience full-blown symptoms of irritable bowel syndrome (IBS) from the consumption of these fructans.