Slicing onions: why does this seem to work?

My brother and my best friend both use a technique for slicing raw onions which involves making a cut across the root stem and then making another opposing cut across that cut (an “X”). I tried this and, as they said, it does seem to considerably reduce the lacrimosity (tearfulness) of onion slicing. Anyone have an idea why this works?

Not quite getting the picture of the cuts you are describing . . . But . . .

If the object is to minimize lacrimosity (which I suspect should be spelled lachrymosity, actually):

A friend (former roommate) and I once wondered about this, 30-some years ago: Is onion lachrymosity caused by the fumes you inhale up your nose, or by the fumes that waft directly into your eyes?

This was tested by the device of wearing a pair of goggles while cutting some suitably lachrymous vegetables.

The conclusion: It’s the fumes that get into your eyes. Wearing goggles greatly reduces this.

I hear cutting near an open flame helps.

Or cut with your eyes closed.

Which reminds me… I’m out of bandages…

It helps for the onions to be cold, as this reduces the volatility of the tear-inducing compounds. Put them in the fridge for a while before slicing them. It also helps a bit to use a really sharp knife - a dull knife will crush the cells and release more juice.

One thing I’ve noticed that seems counter-intuitive is that I have much more of a problem with irritated eyes if I’m wearing glasses than I do if I’m wearing contact lenses when I cut onions. I can only conclude that the sclera doesn’t react, only the iris/cornea.

From what I’ve read, sulfur compounds released by the onion (and not released as much when the onion is cold, so refrigerating/freezing also helps) react with the water on the surface of your eye to form a very dilute sulfuric acid, hence stinging and tearing. Since my eyes seem especially susceptible to this, I bought lab goggles. And yes, they work great!

(I long ago stopped trying to make soap at home, or I’d still have lye around somewhere. And I have long, sturdy rubber gloves for homebrewing. Really, it’s like a sitcom setup for a mistaken police raid, especially with the popularization of the term “cooking” for drug-making among the general public in the wake of Breaking Bad.)

Oh, and count me among those who can’t picture what the OP is describing, but I seem to recall people alleging that the root end had the highest sulfur compound concentration and should be left for the end?

For those who can’t picture what the OP describes, it’s just scoring the root-end of the onion with an “X” shape.

I can confidently say that this has about zero effect on the degree to which the compounds in an onion affect you.

Someone on NPR said that a chemical reaction begins when the onion is cut. Henceforth, I began slicing off the top and bottom, peeling the onion and leaving it for a few minutes. I thought I was successful because I waited for the reaction to cease, but now I wonder if it because I cut off the bottom and top first.

As I said, I tried it (two shallow cuts all the way straight into the root-stem part in an “X”) and it seemed to work. One of the onions I cut this way was one of those nasty yellow ones that really sting. Perhaps the cuts draw the irritant into to root area?

I don’t slice onions but have heard a tip that slicing them under water in the sink will eliminate tearfulness completely.

I’ve seen that on the web, trying to document my “Wait, already!” theory, but it’s difficult to dice them that way…they keep floating away.


That works because the fumes don’t get into the air. But as already pointed out, it’s pretty inconvenient.

Wait a minute.
You pay lady boys to slice your onions?
You could catch something!

Is that what they’re calling it now?

Going native, are you, Old Boy?


What a layered conversation.

I do the opposite: I cut everything but the root area. I never have any irritation. This was recommended by some chef on the Cooking channel. I don’t remember who.

The main advantage to leaving the root area intact is that it holds the onion together as you’re chopping it.

Refrigerating the onion makes a big difference.

If you have a lot of onion slicing to do, set up a fan nearby to waft the vapors away from your eyes. A computer-style muffin fan is ideal for this.

If you are chopping a slice or two, start with the end opposite the root; that makes the rest of it last a bit longer in storage.