Musty odors are caused by volatile organic compounds. While mold is a common source for these compounds, they can come from other sources. If there is no water anywhere in the basement, then musty odors are probably not caused by mold. If there is water, mold probably plays a role, but may not be the entire problem.
First, let’s talk about mold. Actively growing mold produces a wide range of volatile compounds, some of which can impart a musty odor. Many of these compounds can be detected by the human nose at very low concentrations. The mold colonies do not have to be sporulating to release these compounds, so that nearly invisible mold can be the source. When I see carpeting on a basement floor, I usually assume that it is the source for any musty odors that might be present, even if the carpeting looks new and dry and clean. Removal of the carpeting usually ends the odor problem. Mold does occur behind paneling if the wall is damp, and drying the wall is the only solution. Such drying may or may not involve removing the paneling. In both of these cases, airborne spore concentrations can be very low. This is an indication either that the mold producing the odors is not sporulating, or that any spores that are produced are trapped and not entering the air.
Wet concrete has an odor that could be interpreted as musty. While mold can grow on the surface of concrete, it isn’t always present, and just the dampness may be producing odors. Standing water usually doesn’t result in mold growth, but bacteria may grow and produce volatiles with “musty” odors.
Dehumidification is one means for controlling both mold and the damp concrete odors discussed above. I use a dehumidifier that keeps my entire 1000+ square foot basement odor free, and that drains directly into my stationary washtub. It could also drain into a floor drain. Otherwise, the reservoirs of dehumidifiers have to be emptied regularly, and if they are not, they could become odor sources in themselves.
Finally, some dry environments have a musty odor. One cause of this odor that I call the “Antique Shop Odor” is degradation of paper products and very old wood. Old waxes and polishes could also contribute. I am not aware of publications that discuss the specific compounds that cause these odors. I do know that some people find them objectionable and, for that reason, don’t visit antique shops or even museums with antique collections.
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