Could NASA's secret weapon for cleansing air in space capsules do the same in your home? Back in the early 1980s, while preparing for space missions, NASA sponsored research on the ability of plants to remove chemicals from the air, including many common indoor pollutants such as benzene, ammonia and formaldehyde. The results showed that houseplants did help scrub the air, in part by metabolizing the chemicals and using them as sources of food and energy.

Clearing the Air
Bill Wolverton, Ph.D., the scientist behind much of the early NASA research and author of How to Grow Fresh Air (Penguin, 1997), believes this effect is even more relevant today than it was when he first began studying it. "Houses are more tightly sealed than in the past and contain a higher percentage of synthetic materials and products versus natural products," he says. "These synthetics emit hundreds of ¿ chemicals into the indoor environment." Indeed, the Environmental Protection Agency (EPA) says the air inside our homes is often more polluted than the air outside.

Subsequent research by Wolverton and others supports the initial NASA findings. Later studies also have suggested that plants can help remove dust, pollens and other allergy triggers from the air and help keep humidity at healthful levels. One caveat, though: According to the EPA, simply plopping a lone spider plant on your table isn't enough. Other strategies include making sure your home is well ventilated, keeping the humidity level between 30 and 50 percent, and using fewer household chemicals and bug sprays. The more strategies you employ, the greater the benefit.

The advantages of houseplants don't stop at cleaner air. One study conducted in a computer lab at Washington State University found that systolic blood pressure went down and productivity went up when plants were added to the lab (Journal of Environmental Horticulture, 1996). Workers also felt more attentive. Other studies have shown that people exposed to greenery may have decreased pain levels and improved healing from surgery or illness. That may explain our instinct to take a plant to an ill friend, even if we don't know exactly why.

Soothing the Soul
Virginia Lohr, Ph.D., lead author of the computer lab study and a horticulture professor at Washington State University, believes the salutary effect of plants may be explained by something known as the Biophilia Hypothesis. This intriguing idea, put forward by Harvard University biologist Edward Wilson, maintains that people have an innate inclination toward other forms of life. An attraction to certain natural environments provided a survival advantage for our ancestors, and they may have passed on to us a preference for lush, green landscapes. Put simply, Lohr says, "We're attracted to habitats that are good for human survival. When we're in these places, we feel better." And as research increasingly suggests, houseplants can stimulate this feel-good response.

To bring more nature into your home, any type of plant will do. In fact, finding varieties that resonate with you and suit your lifestyle is part of the fun. Your neighborhood Publix has plenty of plants to pick from. Whichever you choose, you'll be doing yourself a favor by making plants part of your inner space.