Let’s say a healthy person lived for several decades in an environment of rampant mold and mildew - clothing, walls, carpet, surfaces, etc. The mold/mildew cannot be killed. There is no option of relocating to a mold/mildew-free environment.
Would he or she develop immunity? Develop severe vision/respiratory issues? Die? Body would "ignore the mold/mildew?
Certain kinds of mold can cause cancer with constant exposure.
Most mold and mildew is harmless unless the person has an allergy to it.
A lot of the mold and mildew hysteria comes from companies that can make a profit from cleaning it up.