Everyone knows that they have to clean their carpets and other flooring surfaces to remove dirt, sand, hair, staples, spills and other debris. What they don't realize is that above their heads, those nice out of sight, out of mind ceiling tiles are continually absorbing not only noise, but also atmospheric contaminants such as dust, skin dander, molds, bacteria, viruses, pollens and other allergens. Additionally, in cooking or smoking areas, there is a buildup of grease, oils and/or nicotine.
Most contaminants are lighter than air, so as warm air rises, they have a tendency to flow upwards and settle on the tile surface and in fissures (small holes designed for appearance and sound absorption). Most of these particles are microscopic, so the tiles may appear normal or just slightly discolored over time. The contamination may only become apparent when a new tile is inserted or a test clean is performed. The first visible signs are around air vents where the maximum airflow causes the larger particles to settle on the tiles directly surrounding the vents.