A study has found that female friends who dwell on each other's problems show an increase in stress hormone cortisol and in activity of the sympathetic nervous system.
However, talking over problems without dwelling on them resulted in no such spike, suggesting that compassionate conversation is helpful - when done right.
"Too much of a good thing is a bad thing," study researcher Jennifer Byrd-Craven, an Oklahoma State University psychologist, told LiveScience.
"Really focusing on negative feelings is probably bad overall for your physical health as well as your psychological health."
Earlier studies had shown that excessively rehashing problems with friends - a phenomenon called 'co-ruminating' - seemed to make people more anxious even as it brought the friends closer together.
To investigate this paradox, Byrd-Craven recruited 44 pairs of college-age female friends.
The women completed questionnaires designed to reveal their temperaments and problem-solving styles.
Then the friend pairs were asked either to sit and discuss problems or to work together to plan a community recreation center.
The center-planning task was a control so the researchers could compare problem-talking with a more neutral interaction.
Before and after the tasks, the women gave saliva samples to measure levels of cortisol and salivary alpha-amylase, a compound that signals the activation of the sympathetic nervous system.
The women who planned the community center showed no stress response, and neither did women whose natural problem-discussing style focused on solutions.
But friend pairs who ruminated on their problems, discussing them without any resolution, showed an increase in both cortisol and salivary alpha-amylase.
The study looked only at the short term, so researchers don't know how co-ruminating affects health over the long term. But preliminary evidence suggests the answer won't be a positive one.
"Other studies have shown that dual stress system activity is related to the highest risk for internalizing symptoms. So, depression and anxiety," said Byrd-Craven.
One odd upside to co-rumination is that women who do it report being closer to their friends, she said.
The next step is to look at how the women and their friendships fare in the long term, and to see whether people can learn to talk about problems in a more effective way, she added.
The results are published in the Journal of Social and Personal Relationships.