Why Do Onions Make Us Cry
There’s no question that onions are good for you. They’re one of the five foods most commonly associated with longevity, they contain fiber, potassium, folate, manganese, copper and more than 100 other phytochemicals, and research suggests they may reduce risk of cancer, heart disease and Alzheimer’s. But there’s another reason people love them — their smell.
Onion odor has been described as “sweet,” “musky” or even “mildly sulfurous.” And it turns out, this pungent aroma contains compounds that trigger a specific brain reaction when inhaled. The result? Tears.
The science behind why cutting a raw onion causes us to cry isn’t exactly clear. When an onion is cut, an enzyme called allinase is released from the broken cells, converting the amino acid alliin (a nonproteinogenic amino acid found only in plants) into a substance called allicin. Allicin then combines with oxygen molecules to form a reactive compound known as thiosulfinate. This chemical irritates sensory nerve endings located on the roof of your nose and just under the eye, triggering the release of neuropeptides like oxytocin and vasopressin. These chemicals act as neurotransmitters, carrying signals from one nerve cell to another, and can cause tear production by stimulating nerves in the lacrimal gland. When exposed to such strong smells, the eyes secrete tears to wash away the offending odors and we begin to cry and smart.
So what does all this mean for those who would eat an onion without crying themselves sick afterward? According to researchers at Johns Hopkins University School of Medicine, the answer is maybe nothing. After looking at previous studies conducted over the past 60 years, the team concluded that eating raw onions doesn’t increase your chances of developing asthma, hay fever or other allergic reactions. It also doesn’t appear to affect children younger than age 6, according to results published online Jan. 23, 2014 in JAMA Pediatrics.
This latest study was sparked by some pretty interesting findings regarding allergies among young children. For example, while kids ages 4-5 have lower rates of food allergy than adults do, this trend reverses itself after age 8. Researchers believe this might be due to a combination of factors including genetics, environment and diet. In particular, scientists think early exposure to certain types of bacteria could play a role in preventing food allergies, which led the researchers to wonder if changing diets early in life could help prevent allergies later on. To find out, they studied data collected between 1963 and 2009 by the National Health Interview Survey, which monitors health conditions and behaviors across the U.S. population annually through personal interviews.
While many prior studies had looked at how often people ate raw vegetables, few had examined whether doing so increased the chance of developing allergies. So the authors divided participants’ consumption habits into four categories: never eats raw vegetables; eats cooked/eat raw vegetables; mostly cooks vegetables; rarely cooks vegetables. Then, using self-reported information about symptoms related to food allergies, the team ran statistical analyses to determine if these patterns were linked to higher incidences of allergies.
Of the almost 20,000 people included in the study, 5 percent reported having hay fever. Of those, 15 percent said they’d eaten raw onions recently. Those who ate onions three times per week or more were nearly twice as likely to develop hay fever compared to those who didn’t consume onions at all. People who consumed raw onions monthly or less frequently but ate cooked onions weekly or more had similar levels of hay fever incidence.
For those who don’t get much joy from cooking, the next best thing may be to roast them whole. Roasting increases the amount of allyl sulfide produced, making the resulting flavor more intense. Additionally, roasting the bulbous base of each individual onion before slicing it will give you sweeter slices because the outer layers are removed. Finally, if you need to make a quick sauce or soup, sauteing the sliced onion first will let the flavors come together faster.
If you must remove the skin, however, try removing it by holding the peeled onion against a bowl filled with ice water. As long as you hold it up close enough to the ice, the heat will stay below danger zone.
In addition to onions, garlic also triggers tears. While its effect on humans isn’t well understood, it seems that it works along similar lines to onions. Specifically, the smell of fresh garlic activates special receptors in the olfactory system, causing the same reaction — tearing eyes — as its counterpart.
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