The phenomenon of tearing up when cutting onions is a common experience for many people, but not everyone experiences it. The reason why some people do not cry when cutting onions has to do with individual differences in sensitivity to the compounds released by the onion.
When you cut an onion, it releases a volatile gas called syn-propanethial-S-oxide. When this gas comes into contact with your eyes, it forms a weak sulfuric acid, which irritates the eyes' tear glands. As a result, the tear glands produce tears to flush out the irritant.
People who don't cry while cutting onions may have:
Less sensitive tear glands: Some individuals have less sensitive tear glands, so the irritation caused by the onion's compounds doesn't trigger a significant tear response.
Familiarity and repeated exposure: Frequent exposure to cutting onions might desensitize some individuals over time, leading to a reduced tear response.
Eye protection: Some people may unconsciously blink more or use a specific cutting technique that minimizes the contact between the onion's gases and their eyes.
Genetic factors: There could be genetic variations that influence how sensitive a person's eyes are to the irritants released by onions.
It's essential to note that not tearing up when cutting onions is harmless and nothing to be concerned about. However, if you suddenly start experiencing tearing when cutting onions or any other unusual eye-related symptoms, it might be a good idea to consult an eye specialist or a healthcare professional for a check-up.