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.
Raw onions can cause irritation to skin, mucus membranes and eyes. This is due to release of allyl sulphide gas while chopping or slicing them. The gas when mixed with moisture (water), converts into sulfuric acid. Allyl sulphide is concentrated more at the ends, especially at its root end.