Cutting onions is a notorious trigger for tears, a phenomenon that has puzzled many. The reason behind this lies in the natural defense mechanisms of the onion. Found beneath the soil, onion bulbs are a target for various subterranean creatures, such as voles, which have a penchant for feasting on bulbs, tubers, and roots. To ward off these hungry predators, onions have developed a unique protective strategy.
Upon being cut and their skin breached, onions release a combination of sulfenic acid and enzymes. These substances react to form a volatile gas known as propanediol S-oxide, which is a lachrymatory agent – a compound that induces tears upon contact with the eyes. This gas, when it meets the moist surface of the eyes, transforms into sulfuric acid, further irritating the eyes, Via NPR.
The human eye, equipped with its own defense system, responds to such irritants by producing tears to flush out the offending agent. This natural response varies among individuals, with some people being more susceptible to the tear-inducing effects of onions. Those with allergies or sensitivities to onions and related alliums may experience more intense reactions, including tingling, itching, or the appearance of hives.
The tear-inducing potency of an onion is also influenced by its type. Varieties rich in sulfur compounds, such as white, red, and yellow onions, are more likely to cause a strong chemical reaction and, consequently, more tears. In contrast, sweeter onions like green onions have lower sulfur content, making them less pungent and less likely to induce tears.
Advancements in crop science have led to the development of tear-free onion varieties, such as Sunions, which are available in select specialty markets. These genetically modified onions offer a less tearful chopping experience but are not yet widely available.
While onion-induced tears are harmless, they can be a nuisance. Various remedies can alleviate the discomfort, including keeping a distance from the cutting board, rinsing the eyes with cool water, using lubricating eye drops, applying cold compresses, or employing other sore eye treatments.
Food scientist Dr. Abby Thiel suggests additional strategies to minimize tears, such as using a fan, wearing protective goggles, chilling the onions before cutting, increasing ventilation, lighting candles, or introducing acids to the cutting environment. Proper cutting techniques, using water to reduce vapor release, and shielding oneself from the vapors can also help prevent the tearful response associated with chopping onions.
