When things smell moldy -- it could be clean clothes left in a heap, a damp basement, old books stored in elevated humidity -- they can smell moldy.

There are distinct smells for each of these.

Are we smelling the mold spores themselves, or are there other molecules released by molds that causes the "moldy smell" we perceive?


1 Answer 1


The vast majority of the things you smell are odorants, or volatile molecules; not spores. They are light compounds that have high vapor pressure (are airborne), and that interact with your chemoreceptors in your nose (can be smelled). The most-often reported microbial volatile organic compounds in living environments according to this study are as follows:

  • 2-Methyl-1-propanol
  • 3-Methyl-1-butanol
  • 3-Methyl-2-butanol
  • 2-Pentanol
  • 3-Octanol
  • 1-Octen-3-ol
  • 2-Octen-1-ol
  • 3-Methylfuran
  • 2-Hexanone
  • 2-Heptanone
  • 3-Octanone
  • 2-Methylisoborneol
  • 2-Isopropyl-3-methoxy-pyrazine
  • Geosmin
  • Dimethyl disulphide

Geosmin is probably the most moldy-smelling and is detected very sensitively by olfactory systems of animals that want to avoid contaminated food. To me it smells muddy, or earthy, like soil after a rain shower. In our lab, about half the people find it a pleasant smell. It can be smelled in wine, it's the earthy taste found in vegetables, it's the smell of dead bacteria, and so on and so on. The term petrichor describes the odor and geosmin is a major contributing odorant for this.

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    $\begingroup$ Of course, this is just a shortlist of the major odorants. There exist hundreds if not thousands of other volatiles that are released by microbial life. And very often, the mixtures/proportions of odorants can be useful for the perception of smell; it need not be a single compound that makes things seem moldy. $\endgroup$
    – S Pr
    Jul 22, 2019 at 11:11
  • $\begingroup$ Okay this is really interesting, I'll get a hold of the paper soon and give it a read. I've about VOCs in the past in the context of air pollution and air quality, but this is the first time I've heard of MVOCs! $\endgroup$
    – uhoh
    Jul 22, 2019 at 11:46
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    $\begingroup$ I believe geosmin is from bacteria, not mold, and at least the sources you cite are consistent with that. Therefore, geosmin doesn't really seem to answer the question, unless you can support a suggestion that "moldy smell" is unrelated to mold. Also the hypotheses I have heard about geosmin sensitivity are related to the importance of fresh water in a fairly arid environment, not detection of food contamination, hence the pleasant perception. $\endgroup$
    – Bryan Krause
    Jul 22, 2019 at 16:11
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    $\begingroup$ Geosmin is abundantly released by moldy fungi. It's microbial, not strictly bacterial in origin. I defer to any and every textbook on the topic, or a quick google search. I also work with it in the context of insect ecology :) $\endgroup$
    – S Pr
    Aug 8, 2019 at 14:09
  • $\begingroup$ not sure if this is relevant but I just ran across it today by accident mVOC 2.0: a database of microbial volatiles. $\endgroup$
    – uhoh
    Dec 17, 2022 at 1:33

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