There are long-standing urban legends and old wives' tales regarding flowers and the sick.

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In the "get well soon" world, flowers are the go-to gift. They brighten up a dull room, bring some nature into the picture and are just plain good at cheering people up -- which makes it all the more strange that lots of people think flowers should never be placed in a hospital room. Some hospitals even have rules to that effect. San Antonio Community Hospital, for instance, has the following statement on its Web site: "For the health and safety of all patients, flowers and helium balloons are not permitted in cardiac and intensive care units" [source: SACH].

The belief is fairly entrenched, and it goes back a good ways. The urban-legend experts at Snopes have traced it back to 1923 in print form, and it most likely spread via word of mouth long before that [source: Snopes]. The myth goes like this: Flowers are bad for hospital rooms because they suck oxygen out of the air. And sick people need their oxygen.

This oxygen-sucking myth is just one of many longstanding beliefs regarding flowers and ill health. An old wives' tale common in England states that if you put red and white flowers in a single vase in a hospital room, a person in the surrounding ward will pass away [source: Snopes]. Another common legend goes that patients should always leave flower arrangements behind in the hospital room when they're discharged; if they bring the flowers home, they'll end up right back in the hospital [source: Snopes].

The difference between these myths and the oxygen-depletion belief is that the latter seems to have a scientific explanation. But is it really any different?

In this article, we'll look at the belief that flowers are bad for hospital rooms. We'll find out whether the science is sound, and look at other evidence of flowers' effects on sick people.

So, what's the truth about cut-flower arrangements and air composition?