Why Asparagus Makes Urine Smell?

The smell come from the way certain chemical compounds in asparagus break down inside peoples bodies.  As to this specific resulting chemical compound, since 1891 it was thought to be caused from methanethiol which is a colourless gas that smells a bit like rotting cabbage.  However, research in 1975 using a gas chromatography-mass spectrometry concluded that it was actually from the s-methyl thioesters, s-methyl thioacrylate and s-methyl thiopropionate. Thioesters, like methanethiol, are primarily sulfur based except being formed from sulfur bonding with an acyl group.  So, essentially, as with the garlic, a type of sulforic compound is the culprit.