Editor’s Note: This article was originally published in May 2009 and has been updated for accuracy and completeness.

The indoor pollutants that affect health are formaldehyde, Volatile Organic Compounds (benzene and trichloroethylene or TCE), airborne biological pollutants, carbon monoxide and nitrogen oxides, pesticides and disinfectants (phenols), and radon. These pollutants contribute to ‘sick building syndrome’, which causes symptoms ranging from allergies, headaches and fatigue through to nervous-system disorders, cancer and death.

Through studies conducted by NASA, scientists have identified 50 houseplants that remove many of the pollutants and gases mentioned above. NASA, with assistance from the Associated Landscape Contractors of America, conducted a two-year study directed by Dr. B.C. Wolverton, an environmental engineer from Picayune, Washington, and a research scientist for NASA for over 20 years. Dr. Wolverton’s study of the interaction between plants and air found that houseplants, when placed in sealed chambers in the presence of specific chemicals, removed those chemicals from the chambers. He concluded that plants can clean pollutants in homes, offices, factories and retail outlets.

Later, Wolverton expanded the study and assigned plants a rating from one to 10, based on a plant’s ability to remove chemical vapors or indoor air toxins, ease of growth and maintenance, resistance to insect infestation, and the rate at which water evaporates from the leaves. He summarized much of his research in his book, “How to Grow Fresh Air – 50 Houseplants that Purify Your Home or Office.”

Here are some details about the highest ranking houseplants in that study.

Top ten indoor plants for removing formaldehyde, benzene, and carbon monoxide from the air: