As modern weather-proofing techniques make homes more air- tight; pollution from household chemicals such as cleaning agents are becoming an area of concern, due to the health hazards they may pose. In the past, these internal air pollutants were of little concern, because their noxious gases could escape through cracks and crevices or through the heat or ventilation system. Today, many of these 'escape valves' have been plugged to prevent the escape of heat, resulting in increased air pollution. 

Green thumbs, however, may have little need for concern. Scientists at the National Space Technologies Lab in Mississippi have tested several houseplants for their ability to clean the air, including such common houseplants as the Spider plant, the golden pathos, and the Chinese evergreen. Their research showed that a spider plant sealed in a chamber with formaldehyde can reduce the concentration by 85% in 24 hours; while other pollutants that plants were found able to cleanse from the air included carbon monoxide and nitrogen dioxide. However, scientists speculate that as few as 15 plants in an average size house might significantly cleanse the air.