The composition of tears caused by emotion differs from that of tears as a reaction to irritants, such as onion fumes, dust, or allergy. Propanethial S-oxide is a sulfur chemical that is a gas that floats through the air and into your eyes. Stable molecules in the onion’s tissues transform into a volatile, sulfur-containing gas. When you start cutting an onion, it disrupts the cells and the normal cell enzymes mix with the sulfenic acids and it produces propanethial S-oxide. When you cut into an onion, the synthase reacts with the sulfur to create a chemical compound called syn-Propanethial S-oxide. Onions contain amino acid sulfoxides that form sulfenic acids in the onion cells. The other chemical found in emotional tears is leucine-enkephalin, an … Why Chopping Onions Makes You Cry. Thus, reducing the “tear” effect caused by the cutting onions. Peeling, cutting or crushing an onion's tissue releases enzymes called allinases, which convert these molecules to sulfenic acids. Kat Arney. In “Why Do Onions Make You Cry” by the American Chemical Society video series Reactions, the narrator explains why onions and other allium plants have such a strong odor and why onions, in particular, cause tears when cut. Sulfuric acid can lead to itching, burning — and tears. This gas floats up from the chopped (or bitten) onion and deters critters (and causes humans to shed tears). However, it is a volatile compound i.e. The chemical compounds released by the onions are allyl sulfide and they also exist in garlic and spring onions. Adrenocorticotropic hormones are also common and indicate high stress levels. Propanethial-S-oxide is the major cause of the flavor and aroma of onion. Grab a knife and slice into an onion, and you’ll quickly feel a stinging sensation and tears starting to flow. The cause of tears and itching is the chemicals produced by onion (Allium cepa).Lets go into some details. The sulfenic acids, in turn, spontaneously rearrange to form syn-propanethial-S-oxide, the chemical that triggers the tears. Irritation to the tear glands causes it to secrete tears continuously without being influenced by the intent and emotion to cry. How Crying Works. This compound is volatile and creates a gas that floats up to your eyes and triggers your … When its vapors reach the eye, it causes tears because of being a lachrymator ( aka tear gas) i.e. Simply peeling an onion won’t make your eyes water. Why onions make us cry. vaporizes very quickly. Interestingly, none of the compounds that cause these effects are present in the intact onion; rather, when the cell walls of the onion are damaged by chopping, an enzyme released produces a range of compounds as a defence mechanism, which act as irritants. Acid Effect. Chemicals in tears. The onion (Allium cepa L., from Latin cepa "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium. Enzymes that were kept separate are now free to mix with the sulfenic acids to produce ​propanethiol S-oxide, a volatile sulfur compound that wafts upward toward your eyes. Cutting an onion bursts its cells, producing a chemical process which releases the contents of those cells into the immediate atmosphere, causing you to tear up as you slice and dice. This gas reacts with the eyes to form small amounts of sulfuric acid. Amino acid sulfoxides form sulfenic acids. Unstable chemicals. Onions make us teary because a reaction in the onion releases a chemical called lachrymatory factor, or LF, that irritates our eyes. What kind of chemical does onion have that causes the eyes to produce tears? Onions make us teary because a reaction in the onion releases a chemical called lachrymatory factor, or LF, that irritates our eyes. Slice into it and you unleash a chain of chemical reactions, he notes. Physiology Chemical composition. They likely won’t provoke as many tears as some other onions might. Why Do Onions Make Us Cry? Onions are a vegetable that belong to the plant genus allium. Scientists used to blame the enzyme allinase for the instability of substances in a cut onion. ... or what makes you tear up." Onions contain amino acid sulfoxides that produce sulfenic acids inside the cells of the onion.