Biological pollutants are living organisms that can travel through the air and are often invisible.

Conditions that support biological pollutants growth can be found in many locations, such as bathrooms, damp or flooded basements and or crawl spaces, wet appliances (such as; humidifiers or air conditioners), and even some carpets and furniture.​Studies show that as much as 75% of all structures have damp conditions which may encourage the growth and buildup of biological pollutants.