Onion with tears
Credit: Photo: Getty, Graphic: Kitchn

Cutting Onions Makes Me Feel Like I’m About to Black Out, So I Went Down a Rabbit Hole to Find Out Why

published Sep 25, 2020
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The following story does not provide medical advice. If you have concerns, please consult your doctor.

“Extreme reaction to chopping onions.” “Blacking out chopping onions.” “Chopping onions feeling faint.” These are some of the Google searches I’ve made in an attempt to find out why everyone else cries when chopping onions while I feel like I’m going to pass out. 

It wasn’t always this way. I used to chop onions and get teary. I’d run to a window for air or leave the room, but nothing too out of the ordinary. I could still cook recipes that called for onions without immediately knowing I’d have to leave them out. It wasn’t until five or so years ago that things took a turn. All of a sudden, I’d get two slices in and couldn’t physically keep my eyes open. I’d feel like I was blacking out. Like I was going to faint. Like someone was pushing down on my skull and I was going to fall over. Dramatic, I know. 

I’ve found very few accounts like mine online. The ones that do exist are in random message boards. I started only using shallots. Smaller onion, smaller response is what I presumed.  

Here’s What the Experts Have to Say About This Strange Reaction

“Your reaction is one of the worst that I’ve heard, Dr. Avnish Deobhakta, an ophthalmologist at New York Eye and Ear Infirmary of Mount Sinai, tells me over the phone. “The most famous reaction that onions have on people is that they cause you to start to tear up. But if you think about the pathway and how it works, it’s not out of the question that you could have this experience.” This is good to hear, because I am having this experience.

“Onions release a chemical that is very specific that targets the cornea, and the cornea has a ton of nerves,” Dr. Deobhakta explains. That chemical is syn-propanethial-S-oxide, a sulfur compound. It’s the thing that makes most people tear up, but makes me (and others? Tell me there are others!) feel like we’re going to pass out. 

“The way [cutting an onion] makes you cry is that it basically sends a message through something called the autonomic nervous system, which is a part of the body that is involved in a ton of other different things.” These include fainting and blacking out. Dr. Deobhakta explains that the autonomic nervous system relays information back to the eye, targeting the lacrimal gland. The lacrimal gland is in charge of tears, which wash the “offending agent” — the syn-propanethial-S-oxide — away. It’s an easy, reflexive, quick thing. For most people.

“The offending agent goes into your eye and immediately you have some kind of reaction that is local,” Dr. Deobhakta explains. “It doesn’t go to the central nervous system. It doesn’t go to the brain. The cleanup team is right there ready to go …  it’s a reflex, so to speak. It doesn’t involve the pathways you’re talking about, but [your case] does.” He theorizes, “It strikes me as something where your autonomic nervous system or your sympathetic nervous system is just going into overdrive for whatever reason and that can be causing this.”

Chemist and University of Albany professor Eric Block, who literally wrote the book on onions, relates this to nociceptors, pain receptors that alert the body to potentially dangerous stimuli. “In particular, a receptor known as TRPA1 senses chemical irritants in the air such as tear gas, smoke from a fire, pepper spray, and the irritants from pepper, onion, and garlic,” Block explains. While he points out that he’s not medically trained, Block says, “In my opinion your pain-sensing nerves may be more sensitive than for others. Alternatively the signaling from your chemical-sensing nerves for some reason triggers an unusual response.”

Dr. Jaclyn Kovach, an associate professor of clinical ophthalmology at the Bascom Palmer Eye Institute, explains the following in regards to reactions to onions: “The irritation and tearing are temporary and have no lasting or permanent effects on the eyes. But some people are more sensitive to the gas than others.”

I Haven’t Always Had This Reaction. Why Now?

So, it’s become clearer how this is happening to me, but not why it is happening to me. Obviously, my response is particularly strong, but humans do have varying levels of reactions to onions.

“I literally couldn’t be in the room while onions were being chopped!” Leslie Stephens, an editor who is currently VP of Content for Cupcakes & Cashmere, tells me via email. Stephens’ reaction to onions has moved in the opposite direction as mine: She was highly sensitive and now isn’t. “At the height of my sensitivity, I worked as an editor at Food52 where we had a test kitchen, and any time onions were chopped, I could feel them from across the office,” she continues. “I never blacked out, but if I got within a few feet of the onion chopping, my eyes would water and sting and my nose would run, almost like with bad pollen allergies. The worst part was that it took as long as 15 minutes for the symptoms to stop.” 

Dr. Deobhakta says that the changes we’ve both gone through could be in line with someone developing an allergy they didn’t previously have or building a tolerance to a substance. Like with puberty, for instance, “We change in terms of how we respond to stimuli.” 

Anyone looking for ways to chop onions without crying — or worse — can try a variety of tips. Stephens wrote an article about using a very sharp knife. Dr. Kovach suggests turning on a kitchen hood vent, chilling the onions first, or wearing goggles. Dr. Deobhakta wonders what would happen if I put on an N95 mask. Try any of these at your own risk: A sharp knife might be good enough for some, but leave still others running for an open window while their head pounds. 

As for those shallots, there’s an explanation for why they don’t bother me as much. “White, yellow, and red onions tend to be more aggravating to the eyes compared to sweet onions, green onions, and scallions,” says Dr. Kovach. Block explains that scallions and shallots “contain lower levels of the precursor to the lachrymatory factor, so you would tear less when cutting these plants.” Dr. Deobhakta basically confirms what I thought: Smaller onion, smaller response. 

So, is it just me and the few people on the message boards who think we’re going to pass out in our kitchens when we slice through an onion? “It wouldn’t be surprising to me if we polled all 300 million Americans, and there’s some decent subset of people that would share your situation,” Dr. Deobhakta says. Why don’t we hear from them? They probably just stopped chopping onions.