There are several indicators that your indoor humidity levels are causing mold growth.   If you experience one or several of these indicators on a constant basis in your home, office or school, it's most likely that you have a moisture issue:

• Foggy condensation on the windows.  Windows can be fogging for two main reasons, one of those can be that the seal on the window has broken.  In this case, you will see fog "INSIDE" the two window panes.  However, if the condensation is on the inside of the window, you need to do more discovery inside the home to discover the cause of the moisture intrusion.  The 2nd one is more serious because this is the one that will grow hidden mold.
• Mildew-like smell, especially on fabrics.  Not ALL molds smell.  In fact, some of the most dangerous molds have "no smell" whatsoever.  But if you do smell a musty type of odor, be sure that you definitely have a humidity issue fueling mold growth that is releasing mycotoxin and VOC's that you are smelling.
• Spots of mold growing on the walls.  You'd think this would be the most obvious to people, however with the hundreds of clients I see every year you'd be surprised that people literally aren't alarmed by small mold growth or even large mold colonies more than a 5 ft. radius.  It's pretty astonishing how little people know about the dangers of mold.
• Materials like wood or stucco easily crumble.  The common myth about crumbling wood or stucco is that it's just blown off as "wood rot" or "stucco rot".  It's not taken as serious as it should be.  If that particular spot was sampled and evaluated in an accredited lab, people would find more toxicity exists than they thought.

• Floorboard Signs.  Wood and even MDF floorboards are particularly reactive to changing humidity levels. If your home is dry and the humidity is controlled, the floorboards for the most part, will stay flat and flush against the wall and be nice and smooth. If floorboards are swollen, separated, cracked, stained, or coming loose, this could be potentially an age issue -- or it could possibly be a signal that you need to do more inspection for a moisture issue.

• Paint chips off of the wall easily.  When you see buckling in the paint, it's a clue that moisture is penetrating the drywall "behind" the paint itself. 
• Intense allergies.  Mold "allergic reactions" can include: burning eyes, sneezing, itching face or skin, runny nose/itchy nose/stuffy nose, draining sinuses, dizziness, off balance, ear infections, gook in your eyes, sore throat, lingering cough, skin rashes and more......
• Excessive moisture bugs.   Some bugs are dependent on moisture for survival. Some of these bugs can live in the house if they find sufficient humidity and food.  Silverfish, Termites, Earwigs, Mosquitos, Springtails, Spiders, Drain flies, Cockroaches, Ants, Dust Mites, Book Lice, Fungus Gnats, Mold Mites, Pill Bugs, Centipedes, Millipedes, Crickets, Scorpians, Pseudoscorpians, Bed Bugs, Stink Bugs, Slugs and Flees.
• Difficulty sleeping.  Waking up frequently, agitation during sleep, heart palpitations, sleep apnea, difficulty falling asleep, difficulty waking up in the mornings or you feel like you've never slept.
• Food left out goes bad quickly.  Fruits, Vegetables or Breads seem to show signs of going bad or visible mold on them quickly within days.