Why "old book smell" has hints of vanilla

Stick your nose deep into an old book and inhale deeply. It contains, librarians say, "hints of grass and vanilla," among other smells. The distinctive "old book smell" is so beloved among some readers that there's a parody company out there pretending to sell an artificial spray that makes e-readers smell like books. What accounts for it? As it turns out, dozens of different chemicals that are emitted by paper, binding, ink, and glue as they break down over time. Chemists have conducted a few different studies identifying them. One prominent compound results from the breakdown of lignin, a polymer found in plant cell walls, as well as paper. As it degrades, it's converted into vanillin, a chemical naturally present in vanilla beans, accounting for the hints of vanilla.