There are many potential contaminants that may be present in indoor environments. Some of the more common ones include Dust Pollen Mould spores Bacteria Viruses Animal dander Chemicals (from cleaning products, off-gassing from building materials, etc.) While not all of these contaminants are necessarily harmful, they can certainly cause discomfort or aggravate pre-existing conditions such as allergies or asthma. It is important to try to keep indoor spaces as clean and free of potential contaminants as possible. Regular vacuuming and dusting, using air purifiers, and avoiding the use of strong chemicals can help to create a healthier indoor environment.