Narcissistic people get more empathetic, generous and agreeable with age, according to new research into the personality trait. 

But although their unreasonably high sense of self-importance may mellow, they do not fully grow out of it, the study involving more than 37,000 people suggests. 

Those who were more narcissistic than their peers as children tended to remain that way as adults, investigators found.

And there are at least three types of narcissistic behaviour to look for, they say.

What is a narcissist and how do you spot one?

Narcissist has become an insult often hurled at people who are perceived as difficult or disagreeable. 

We all may show some narcissistic traits at times.

Doctors use the term to describe a specific, diagnosable type of personality disorder.

Although definitions can vary, common themes shared by those who have it is an unshakeable belief they are better or more deserving than other people, which others might describe as arrogance and selfishness. 

The work, published in the journal Psychological Bulletin, comes from data from 51 past studies, involving 37,247 participants who ranged in age from eight to 77.

Researchers looked for three types of narcissists, based on behaviour traits:

• Agentic narcissists - who feel grand or superior to others and crave admiration
• Antagonistic narcissists - who see others as rivals and are exploitative and lack empathy 
• Neurotic narcissists - who are shame-prone, insecure and overly sensitive to criticism

They studied what happened to these personality measures over time, based on questionnaires, and found that, generally, narcissism scores declined with age. 

However, the changes were slight and gradual. 

"Clearly, some individuals may change more strongly, but generally, you wouldn’t expect someone you knew as a very narcissistic person to have completely changed when you meet them again after some years," lead researcher Dr Ulrich Orth, from the University of Bern in Switzerland, told BBC News. 

He says some narcissistic traits can be helpful, at least in the short term. 

It might boost your popularity, dating success, and chance of landing a top job, for example. But over longer periods, the consequences are mostly negative, because of the conflict it causes.

"These consequences do not only affect the person themselves, but also the wellbeing of individuals with whom they interact, such as partners, children, friends, co-workers, and employees," he explained. 

Dr Sarah Davies is a chartered counselling psychologist who has written a book on how to leave a narcissist. 

She told the BBC that although people may be arrogant or selfish sometimes, that should not be confused with true clinical narcissism. 

"Narcissists tend to be envious and jealous of others and they are highly exploitative and manipulative," she said. 

"They do not experience remorse or feeling bad, or have a sense of responsibility like other non-narcissistic people do."

She says there has been a boom in interest in narcissism, driven by social media. 

"To some helpful extent - it helps inform more people about it and to bring more awareness of this issue. However, like many mental health terms, the clinical meaning can get lost.

Dr Davies says we should be more discerning with the term.

"I find it much more useful to be specific with naming behaviours and separate them. For example, a friend of mine recently called her ex a narcissist because he had ghosted her after they broke up. 

"Being ghosted [suddenly cutting someone out of your life without explanation] is of course horrible, but he may not have been able to deal with a conversation after their relationship came to an end. It doesn’t necessarily mean he is a raging narcissist. 

"They were together a while and there were no other indications of his 'narcissism'." 

According to Dr Davies, some signs you may be involved with or around a narcissist include:

• Constant drama - a narcissist needs to be needed and seeks chaos and conflict
• No genuine apologies - they never really take full responsibility for their own behaviours
• Blame game - they manipulate and exploit others for their own selfish gains

Dr Tennyson Lee is a consultant psychiatrist with the Deancross Personality Disorder Service, based in the London borough of Tower Hamlets. He said the study was well-conducted and the findings were useful. 

"The good news is narcissism typically reduces with age. The bad news is this reduction is not of a high magnitude.

"Do not expect narcissism will dramatically improve at a certain age - it doesn't. 

"This has implications for the long-suffering spouse who thinks 'an improvement is just around the corner'," he told BBC News.