Carpet acts as a trap for airborne particles grounded through natural gravity.
Many healthcare professionals will recommend the removal of carpet from homes of their allergy and asthma patients; however that thought is based on assumption, when in fact clean, dry, well-maintained carpet actually improves air quality. Check out http://www.carpet-health.org/aa.asp to watch an informational video, read studies, and learn more about how carpeting can improve your indoor air quality.