We all know that feeling: the burning sensation as we slice into a fresh onion, eyes watering and wincing to relieve the stinging. There are claims that home remedies can solve this problem, including burning a candle, putting the onion in the freezer before chopping, or cutting the onion underwater. In this article we will investigate the culprit behind our onion tears and a possible scientific resolution that has emerged in the 21st century.
The teary-eyed response to cutting an onion is due to the chemical syn-propanethial-S-oxide, which the onion has evolved as a defense mechanism against predators. Each cell inside the onion contains a vacuole filled with enzymes  called allinases that convert amino acid sulfoxides that are present in the onion cell to sulfenic acids  (namely 1-propenyl-L-cysteine sulphoxide, or PRENSCO); these are then transformed by another enzyme into syn-propanethial-S-oxide  (Fig 1).When the onion cell structure is broken during chopping, the enzymes are released and are then able to interact with other chemicals inside the onion cell, thus catalyzing the chemical reactions that produce syn-propanethial-S-oxide  (Fig 1).
The strong, spicy odor that onions emit when chopped are surprisingly not the culprit chemical that makes your eyes water. This odor is formed by the condensation of syn-propanethial-S-oxide to form odorous thiosulfanates . Because syn-propanethial-S-oxide is a volatile sulfur compound, it easily diffuses into the air . Your cornea contains nerves that relay information to the larger nerves responsible for touch, temperature, and pain detection on your face . The nerves on your cornea detect the presence of syn-propanethial-S-oxide and send the signal to your central nervous system (Fig 2), which then stimulate the autonomic nerve fibers on the lachrymal glands to produce tears  in order to dilute the syn-propanethial-S-oxide. This is why referred to as lachrymatory compound or lachrymator, which can be defined as “an irritant that causes the eyes to fill with tears without damaging them” .
Adafruit has had paid day off for voting for our team for years, if you need help getting that going for your organization, let us know – we can share how and why we did this as well as the good results. Here are some resources for voting by mail, voting in person, and some NY resources for our NY based teams as well. If there are additional resources to add, please let us know – adafruit.com/vote
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.