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being too clean could impair the skin's ability to heal. The San Diego-based team discovered that normal bacteria that live on the skin trigger a pathway that helps prevent inflammation when we get hurt.

These bugs dampen down overactive immune responses which can cause cuts and grazes to swell, or lead to rashes, according to research published in the online edition of Nature Medicine.

"These germs are actually good for us," said Professor Richard Gallo, who led the research. Common bacterial species, known as staphylococci, which can cause inflammation when under the skin, are "good bacteria" when on the surface, where they can reduce inflammation.

Dweck sent four female research assistants into New York fifth-grade classrooms. The researchers would take a single child out of the classroom for a nonverbal IQ test consisting of a series of puzzles�puzzles easy enough that all the children would do fairly well. Once the child finished the test, the researchers told each student his score, then gave him a single line of praise. Randomly divided into groups, some were praised for their intelligence. They were told, �You must be smart at this.� Other students were praised for their effort: �You must have worked really hard.�

Why just a single line of praise? �We wanted to see how sensitive children were,� Dweck explained. �We had a hunch that one line might be enough to see an effect.�

Then the students were given a choice of test for the second round. One choice was a test that would be more difficult than the first, but the researchers told the kids that they’d learn a lot from attempting the puzzles. The other choice, Dweck’s team explained, was an easy test, just like the first. Of those praised for their effort, 90 percent chose the harder set of puzzles. Of those praised for their intelligence, a majority chose the easy test. The �smart� kids took the cop-out.

In a subsequent round, none of the fifth-graders had a choice. The test was difficult, designed for kids two years ahead of their grade level. Predictably, everyone failed. But again, the two groups of children, divided at random at the study’s start, responded differently. Those praised for their effort on the first test assumed they simply hadn’t focused hard enough on this test. �They got very involved, willing to try every solution to the puzzles,� Dweck recalled. �Many of them remarked, unprovoked, �This is my favorite test.’ � Not so for those praised for their smarts. They assumed their failure was evidence that they weren’t really smart at all. �Just watching them, you could see the strain. They were sweating and miserable.�

Having artificially induced a round of failure, Dweck’s researchers then gave all the fifth-graders a final round of tests that were engineered to be as easy as the first round. Those who had been praised for their effort significantly improved on their first score�by about 30 percent. Those who’d been told they were smart did worse than they had at the very beginning�by about 20 percent.

The researchers would take a single child out of the classroom for a nonverbal IQ test consisting of a series of puzzles—puzzles easy enough that all the children would do fairly well. Once the child finished the test, the researchers told each student his score, then gave him a single line of praise. Randomly divided into groups, some were praised for their intelligence. They were told, “You must be smart at this.” Other students were praised for their effort: “You must have worked really hard.”

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Why just a single line of praise? “We wanted to see how sensitive children were,” Dweck explained. “We had a hunch that one line might be enough to see an effect.”