Comment: it is a very common problem.

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In reply to comment: leaky condos (see in situ)

it is a very common problem.

and yes it is a direct result of stupidity. our society thinks it knows better than I do and they are paying the price for that arrogance.
here is the answer. IAQ is broken into 2 categories. particulate and gaseous. common air filters only address particles not gases.
humidity is a gas. but it is only one of many.
the ONLY way to address gasses is ventilation. but since smoking has been eliminated..... people are plugging them up.
mold is omnipresent. it will grow where it can.
even inside a sealed bag of cheese.... riddle me this. how did it get in there to grow?
answer, it did not, it was already there!