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A large body of research ties access to nature and green spaces to improvements in both mental and physical health, but evidence that indoor plants confer similar benefits is scanty, and any effects that may exist “are probably weaker than those we find with outdoor forms of nature,” said Frances E. Kuo, an associate professor of natural resources and environmental sciences at the University of Illinois at Urbana-Champaign.

Plants absorb carbon dioxide and release oxygen, and a 1989 NASA study suggested houseplants and their root systems, soil and bacteria absorb indoor pollutants like benzene, trichloroethylene and formaldehyde. But having houseplants is unlikely to lead to significant improvements in indoor air quality and there is a potential downside since plants produce allergens that can elicit immune responses that can be severe, said Thomas Whitlow, an urban ecologist at Cornell University.

That said, several small studies have found health benefits associated with indoor plants. A small 1998 Norwegian study reported that workers had fewer complaints of fatigue, cough, dry throat and itching when they had plants in the office, and experiments in England and the Netherlands found that employees in buildings with plants were more productive, had better concentration and greater work satisfaction than those in bare offices.

Two randomized controlled trials reported that surgical patients placed in rooms with plants reported less pain, anxiety, stress and fatigue than patients without plants. Over all, they had lower systolic blood pressure, were more satisfied about their rooms and felt more positively toward hospital workers. One of the studies reported that patients who had their appendix removed used fewer painkillers if they had plants in their rooms.

There is also some research suggesting that flowers make people happy, and that elderly people who receive flowers as gifts report improvements in mood and even memory. But that study was funded in part by the Society of American Florists, as was another study that found flowers made people more compassionate, less anxious and less depressed.