You're out to lunch with a close friend when she reveals she's pregnant. But there's a catch: it's a secret and you can't tell another living soul for at least a month.

So, how do you feel? Happy to be confided in? Or weighed down by the burden of secrecy?

For the first time, researchers have revealed how being asked to keep someone else's secret plays on your mind.

Previous studies have found that at any given time the average person has about 13 secrets of their own, which can affect their wellbeing.

The new research revealed that people also kept an average of almost 17 secrets for others at any one time, which can be both good and bad for them.

Dr Katie Greenaway, from the Melbourne School of Psychological Sciences, and Dr Michael Slepian from Columbia Business School, conducted three separate online studies.

Published in 2018 in the Journal of Experimental Psychology, their paper found that keeping others' secrets had mixed consequences.

They found that being confided in brings relational benefits, but is also a strain.

"The closer one is to the confider, the more one's mind wanders toward the secret, predicting increased feelings of intimacy, but also burden," they write in the paper.

"The more a secret overlaps with one's own social network, the more one conceals the secret on the other's behalf, predicting increased feelings of burden."

Dr Greenaway says the results show how common secrets are and that keeping them is not always easy.

"Secrecy really pervades all aspects of our lives," she says. "It's a big part of our work and personal lives.

"What we generally see is that the more you're keeping it secret from core people in your life, then generally the bigger impact on your psychological wellbeing."

The three studies involved more than 600 participants, mostly from the US, who kept 10055 secrets between them – an average of 16.8 secrets each.

And there was a broad range of secrets kept that covered abortion, work discontent, trauma, theft, sexual orientation, sexual infidelity, sexual behaviour, personal stories, marriage proposals, pregnancy, lack of sex, mental health, lies, illegal hobbies, hidden relationships, habit or addiction, finances, drug use and ambition.

In the first study, participants were asked about how close they were to the person who confided the secret, how many times they'd had to conceal the secret and how often they found their mind wandering to it.

The second study looked at the feelings of intimacy and burden in the context of the participants' social network and closeness to the confider.

And the third investigated mind wandering – which is when people find themselves thinking about something, in this case the secret.

These subjects were told that the function of mind wandering was to work through unsolved problems, which meant people could become fixated on problems with no solution.

Interestingly, hearing about the problem-solving aspect didn't increase their angst.

Overall, Dr Slepian and Dr Greenaway found that being asked to keep a secret had strings attached.

"Given the burden of one's own secrecy, it makes sense that people often seek confidants," the researchers say in the paper. "By making clear that the secret should stay secret, one could hopefully obtain some help while also keeping it a secret.

"People do find themselves on a pathway to burden when they hold others' secrets, through both spontaneously thinking about the secret and having to actively conceal it on the other's behalf.

"But independently and simultaneously, being confided in can give a relational boost, increasing feelings of intimacy."

More detailed research is planned to incorporate how we can help those who feel burdened by secrecy.

Dr Greenaway, Dr Slepian, Dr Elise Kalokerinos, from the University of Newcastle, and Dr Adam Galinsky, from Columbia University, have secured Australian Research Council funding to further investigate how keeping secrets can affect people.

The Australian-based research will use innovative methods such as texting participants in real time to ask if they are thinking about the secret, rather than having them recall their thoughts later.

It will estimate the costs of secrecy, such as social psychological impairments that can cause lost productivity and mental health issues, and test solutions that might reduce them.

Dr Greenaway says those particularly vulnerable to the effects of keeping sensitive secrets include professionals like police officers, therapists, social workers and intelligence officers.

"It's not actually the act of concealing something from people that causes stress it's the act of thinking about that secret day in, day out," she says.

"We want those people to be able to get help with carrying that burden. Some people would really benefit from professional help around dealing with these things."

As for the pregnant friend, Dr Greenaway explains that even happy news can present its own challenges.

Personally, she says her research has helped her deal with secrets like this by focusing on the faith the confider has shown in her and considering the problem-solving aspect.

In this case, that might involve working out how to explain their abstinence from coffee and alcohol.

"If people confide in me, I try to reframe that positively as that person has really trusted me with that information," she says.

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