Why do molds give off musty odors?

The musty odors produced by molds are known by scientists as Microbial Volatile Organic Compounds. (These compounds are abbreviated as mVOCs.) Some mVOCs produce musty and moldy odors, which result from the chemical changes taking place during the mold life process. They are waste products given off by actively growing molds. Health effects such as headaches, dizziness and nausea have been linked to exposure to mVOCs, but research is only beginning. Odors from mVOCs are a sign that mold is actively growing and so may indicate a level of mold contamination requiring remediation.