A new preliminary investigation has shed light on why some individuals are more prone to tearing up when chopping onions than others. The research, led by Professor Thomas Hummel and his team, explored the previously understudied area of 'subjective individual variability in onion tearing and its relationship to chemosensory sensitivity'. Published in the journal Laryngoscope Investigative Otolaryngology, the study recruited over 1,000 volunteers to examine this common culinary phenomenon.
The act of crying when cutting onions is triggered by syn-propanethial-S-oxide, a chemical released into the air. This compound stimulates the trigeminal nerve, prompting the tear ducts to activate and flush away the irritant. While this physiological response is well-known, the extent to which individuals vary in their sensitivity, and whether this links to a broader sense of smell or chemical sensitivity, has remained largely unexplored until now.
Researchers at the institution, which was not specified in the source, asked 1,001 participants to rate their sense of smell, the condition of their nasal passages, their sensitivity to stinging and burning sensations, and their tendency to cry when cutting onions. Alongside these self-assessments, participants underwent psychophysical tests, including identifying odours from imbued sticks, to provide objective measures of their chemosensory abilities.
Intriguingly, the study found a discrepancy between subjective perception and objective reality. Individuals who reported experiencing more tearing when chopping onions also claimed to possess a superior sense of smell. However, this self-assessment was not corroborated by the psychophysical tests. Those who identified as being more prone to onion-induced tears did not perform better on the objective 'sniff tests' compared to those who reported less sensitivity.
These findings align with previous research indicating low correlations between self-reported olfactory ability and objective psychophysical tests. The research suggests that individuals may not be accurate judges of their own sensory capabilities, a phenomenon that could extend beyond smell to other self-assessments. While the study is a preliminary investigation, it has been peer-reviewed and provides a foundation for future research into this everyday experience.