If they stand in the air, they will reabsorb into all soft fibers, including clothing, drapes, carpeting and upholstered furniture, which act as sinks and then release the chemicals slowly and steadily over the next twenty or so years. Biological growths provoke asthma or flu-like symptoms in many people. Molds, mildews and dust mites are the biggest culprits. Molds and mildews grow in areas where moisture has collected and stood from more than a few days. Basements and bathrooms commonly have this problem.
Dust mites are microscopic organisms that feed off of dead human skin.
Many people are highly allergic to their dander. Dust mites thrive in the bedroom and cause most of their mischief there. Proper house sealing and ventilation can prevent many of these problems, including standing moisture and low air exchanges. The basic premise is that like everything else, a building is a system and is ruled by the laws of physics. All air that goes out of a building pulls air into a building to replace it.