1 Pain that does not diminish with rest, and pain that may be worse at night than during the day. 2  Back pain along with constitutional symptoms, such as loss of appetite, unplanned weight loss, nausea, vomiting, or fever, chills or shakes.
Unstable chemicals. Onions produce the chemical irritant known as syn-propanethial-S-oxide. It stimulates the eyes' lachrymal glands so they release tears. Scientists used to blame the enzyme allinase for the instability of substances in a cut onion.
I've sliced into a lot of peaches and hacked apart more than my fair share of lettuce, but none of these foods have been so irritating that my eyes had to wash the resulting chemicals away with bodily fluids. You have to wonder about exactly how toxic an onion is when the gas of it alone makes your eyes tear up.