They can travel through the air and are often invisible. They are usually inhaled, either alone or by attaching themselves to particles of dust and then entering the respiratory system. While the majority of biological pollutants are found indoors, some are of outdoor origin. Bacteria, fungi and molds find nourishment and can flourish in improperly maintained air ducts, air conditioners, humidifiers, dehumidifiers, air-cleaning filters, carpets and in improperly ventilated places where moisture is likely to collect, such as bathrooms, kitchens, laundry rooms and basements. Viruses can be carried indoors by people, while plants, pets and insects are potential sources of pollen, dander, and other allergens.
Dust mites and other insects can thrive in sofas, stuffed chairs, carpets and bedding.
When biological agents are allowed to flourish in poorly maintained ventilation systems, severe health problems can result that can be experienced throughout an entire building. Infectious and noninfectious diseases can be caused by the various biological agents. They can make you sneeze, trigger allergic reactions, cause rashes, watery eyes, hoarseness, coughing, dizziness, lethargy, breathing problems, and digestive problems. People with asthma are especially susceptible to allergic problems caused by biological agents. Their very sensitive airways can react to various allergens and irritants, making breathing difficult.