Teenage girls are particularly vulnerable to co-ruminating  and depression and anxiety  because “there are so many stressors in adolescence and a lot are ambiguous,” Dr. Rose added. “So things like starting dating or starting serious relationships with boys, concerns about cliques, being popular  these very social stressors, they can be really hard to control and they really lend themselves to rumination.”

Dr. Rose first published a paper on co-rumination in 2002, in the journal Child Development, and has, along with other psychologists, continued to study it. In her study published last year, she followed 813 third-, fifth-, seventh- and ninth-grade girls and boys over six months. Researchers at the State University at Stony Brook will soon publish another paper on co-rumination. Both studies confirm Dr. Rose’s earlier findings.

The relationships the experts looked at will certainly be familiar to many teenagers and parents.

Ms. Lee’s daughter Tessa Lee-Thomas said she sometimes felt worse after talking to friends about problems. “Sometimes we get into disagreements,” said Tessa, who lives in Prospect Heights, Brooklyn. “And we have to settle them. My friends think that my other friend did something wrong, but she didn’t do something wrong. Sometimes it makes the situation worse than where we were when we began. It spiraled into something bigger than it was.”

Patricia Letayf, a sophomore at Tufts University, said she tended to overanalyze situations and ask many different friends for advice about the same problem, which at times made her feel more anxious.

“It’s like you want to solve a problem whatever it may be, but the advice of one person never satisfies you and you’re constantly on the hunt for more advice,” she said. “I think a lot of times you are looking for empathy and you want someone to feel the way you do. You want your feelings to be justified. In the end, I hope to feel better. You want them to say, ‘It’s O.K. he dumped you, you failed the test.’ You’re seeking reassurance.”

Ms. Letayf, 19, spent the summer as a camp counselor and said she noticed that the nine-year-old girls at the camp were already starting to obsess about their problems  talking about the boys at the camp and about conflicts between two groups of girls.