Often mold develops beyond being simply an Allergenic or Pathogenic organic.  
Mycotoxins are chemicals produced by molds or fungi. Trichothecenes, Aflatoxins, Ochratoxins, Gliotoxin, Chaetoglobosins and Sterigmatocystin. Where conditions are right, fungi proliferate into colonies and mycotoxin levels become high. Toxins vary greatly in their severity.
Some fungi produce severe toxins only at specific levels of moisture, temperature or oxygen in the air. Some toxins are lethal, some cause identifiable diseases or health problems.  
Some toxins effect the auto immune systems. Some toxins are carcinogenic. It's important to know when testing for mycotoxins is necessary and how to remediate in an effective manner to provide a clean, healthy environment where mycotoxins have been identified.