The cause of narcissistic personality disorder isn’t completely understood but it is thought to be partly down to environment, genetics and neurobiology.
Someone who has experienced either excessive adoration or excessive criticism as a child from their parents may grow up to be a narcissist.
Alternatively, the condition could just be inherited or to do with the connection between the brain, behaviour and thinking.
Narcissistic personality disorder is more common in males than females, and it often begins in teens or early adulthood.
The Mayo Clinic warns: “Keep in mind that, although some children may show traits of narcissism, this may simply be typical of their age and doesn’t mean they’ll go on to develop a narcissistic personality disorder.”