Indoor molds are found mostly in damp areas like bathrooms and around windows, basements, HVAC ducts, damp ceilings and walls, wet carpets and under the house. Poor ventilation is the biggest cause in bathrooms. Exhaust fans can be installed improperly and should be checked if molds are a problem. The most common molds are Alternaria, Aspergillus, Cladosporium and Penicillium. Some of these molds or fungus are also found in many common medicines and foods.
Some molds produce toxins to protect their environment.
The toxins or fungus, when inhaled are a significant cause of common allergic reactions, altered immune function, asthmatic reactions, chronic sinusitis, depression, diarrhea, fatigue, headaches, irritability, liver damage, nose bleeds, respiratory dysfunction, or sore throat. One of the worst molds is called Stachybotrys chartarum, which causes cold or flu-like symptoms. One family suffering because of it tried selling their home resorted to burning it down instead. Schools spend thousands replacing walls and ceilings because of molds. A simple ozone generator would have been a lot less expensive.