In life, certain things can make one cry – death, breaking up, birth of a baby, words triggering strong emotions…and onions. For many, slicing into an onion causes a burning sensation making our eyes water and tear up to make the stinging go away. The average American consumes about 20 pounds of onions a year making onions one of the most widely used foods in cooking.  Very likely many of us (but not all) are affected by onions resulting in a reaction making our eyes swell with tears. 

The reason why onions can cause tearing up or irritation of our eyes can be blamed for a chemical released by the onion called lachrymatory factor or LF.  If you pick up a fresh onion and smell it, there is very little if any smell and your eyes won’t water.  Even simply peeling an onion usually does not result in LF being released.  But if you damage cells within the onion by chopping, cutting or crushing it, the strong, pungent smell of onions is released causing you to tear up. 

The science behind the crying reaction simplistically is this - when the cells of the onion are broken open, this allows two normally separated substances to combine.  Inside the intact cells of an onion are two substances, sulfenic acid and alliinase.  Sulfenic acid is a molecule precursor floating undisturbed within the watery filler of the onion’s cells.  Alliinase is a protein also floating in the cytoplasm in little sacs called vacuoles.  Neither sulfenic acid or alliinase have been introduced yet but once they meet such as by chopping an onion, it sets the process in motion.   

As sulfenic acid and alliinase collide, they fit together perfectly like a jigsaw puzzle.  This connection changes the chemical structure once linked together.  Once connected, they form a chemical or “tear” gas wafting up to the sensory nerves in your eyes resulting in tearing up for some people. Like most plants, think of this chemical formed as an onion’s defense mechanism protecting the onion from microbes and even us as people.  The onion doesn’t want to be messed with but once its cells are broken, the chemical reaction begins hoping to fend off the invader from further damage.

Depending on the variety and sulphur content of the soil grown in, will determine flavor intensity of onions and their ability for making our eyes water.   There has actually been a tearless onion produced by Japanese scientists.  But it lacks the signature onion flavor completely changing the taste. If this is the case, then it may be you just have to put up with being a sobbing mess while chopping away.

If the thought of slicing into an onion makes you want to cry, is there anything one can do to still enjoy the luscious flavoring onions offer to foods without always turning on the tears?  A suggestion by the National Onion Association says to chill onions first for 30 minutes.  Then cut off the top and peel the outer layers leaving the root end intact.  It’s the root end which has the highest concentration of sulphuric compounds making your eyes tear. 

The only drawback is these tactics can also alter the flavor since they impair the processes that produce it, sort of like what happens if you refrigerate tomatoes.  So, take your pick.  Chop away through blurry, tear-filled eyes or have dry eyes but a lackluster flavored dish.