They can cause poor indoor air quality and some can damage surfaces inside and outside the home. These contaminants can travel through the air and are often invisible. Common indoor biological contaminants include bacteria, molds, mildew, viruses, animal dander and cat saliva, house dust mites, cockroaches, and pollen. Bacteria are carried by people, animals, and soil and plant debris. Viruses are transmitted by people and animals.
Pollens originate from plants.
The protein in urine from rats and mice is a potent allergen. When it dries, it can become airborne. The two conditions that are necessary to support biological growth are nutrients and moisture. Mold, mildew and other biological contaminants can grow in contaminated central air handling systems. These systems can distribute the contaminants through the home.