To answer that question you must first understand that mold has two faces;
There’s the face you can visually see (mold growing on a surface), which can cause property damage.
Then there’s the face you don’t see (mold floating in the air), which can cause people damage.
In both cases, the level of damage is directly related to the level of infestation.
Mold you can see
Surface mold has the potential to cause significant property damage.
Molds spores secrete digestive enzymes that decompose the surfaces they live on. For that reason, all mold is bad. The longer mold is allowed to infest any surface, the more damage it can cause. That is why hidden mold is such a tremendous threat. It’s potential to cause damage is devastating because a great deal of time can pass before it is detected.
The visual appearance of mold on construction materials and personal contents indoors is an obvious indication of a mold problem. The pungent mildew or musty odor of mold indoors is another obvious indicator, even when mold is not visibly present. If you suspect you have a mold problem in your home or office, immediate steps should be taken to identify and correct the cause. The longer mold is allowed to grow, the more damage it will cause to your property and the more it will cost to remediate. Prompt action can mean the difference between a few hundred dollars in repairs or several thousands of dollars.
Considering the potential mold has to damage and depreciated the value of property, all molds have the potential to be bad.
Mold you might not see
Airborne mold has the potential to cause adverse health reactions.
Since airborne mold spores are everywhere all the time, indoors and out, we are always exposed to mold at some level. In an open outdoor environment we are seldom exposed to any significant levels of spores because the air is continually moving. But indoors, where ventilation is restricted and air is often recycled through heaters and air conditioners, the exact same molds that don’t bother anyone outdoors can cause severe reactions indoors, especially when levels are exceedingly higher than outside.
When mold is growing indoors, the amount of mold in the air can be significantly higher than outdoors. Exposure to high concentrations of molds in enclosed spaces such as residential homes, commercial buildings, schools, automobiles, airplanes, etc., can trigger asthma attacks, cause respiratory infections, bronchial polyps, and a number of other reactions.
Exposure to extremely high concentrations of airborne mold over extended periods of time can over-come the lungs capacity to filter out spores. Once mold enters the bloodstream the severity of symptoms and reactions increase exponentially.
Considering the potential health risks of airborne mold spores indoors, all molds have the potential to be bad.