Narcissists will often admit their narcissism, but not its adverse effects. If you took them at their word, as researchers did for decades using self-reports, you'd think that narcissists are happier, healthier, smarter, less anxious, less depressed, and more creative than everyone else. But just recently researchers have begun studying narcissists on a physiological level, and these findings paint a different picture.

In one such study, University of Michigan psychologist Robin Edelstein and her collaborators gave undergrads ten minutes to prepare a speech. Students were told that their audience would be composed of human behavior experts—who were, in fact, just observers told not to nod, smile or react when the students presented. Then the researchers took away the students' notes right before their speech so they had to present from memory or off the cuff to a non-responsive audience.

This simple experiment generates a reliable stress response, which causes a surge in the stress hormone cortisol that researchers can measure. You'd think that narcissists' confidence would mitigate their stress. But, in fact, narcissism was associated with increased stress. Though there was minimal difference in cortisol levels among women, in men, higher narcissism predicted greater cortisol reactivity and worse mood. Other research with different experiments shows similar results: narcissists get physically more stressed than less narcissistic people when performing for an audience.

"Narcissism comes with physiological costs," says Joey Cheng, a psychologist at the University of Illinois. In one of her own studies, Cheng measured cortisol and alpha-amylase, two biomarkers of stress produced by the sympathetic nervous system (our fight-or-flight response). Over a three-day period, she found that narcissists produced higher amounts of both markers when they experienced negative emotions in response to everyday frustrations.

"Narcissists' stress-response systems are particularly sensitive to everyday negative emotions," Cheng explains. "Among people who are not narcissists, you don't see this really elevated output of these stress markers." And, interestingly, narcissists had elevated levels of both cortisol and alpha-amylase, which typically aren't strongly correlated. Whereas cortisol reflects immediate, acute stress, alpha-amylase is more associated with long-term, chronic stress. Cheng's research indicates that narcissists may suffer more from both.

But why? What makes narcissists so stressed? For one, narcissists might be more stressed than non-narcissists because they're actually more insecure. Cheng says her research is consistent with the longstanding theory that narcissists are, counterintuitively, less confident and less able to cope with setbacks. What Cheng and others call narcissists' "fragile egos" might explain why they're more agitated by daily hassles. "If they were truly confident and not vulnerable or fragile, they should show the opposite pattern, where they would have less stress entering the body during hardship," Cheng notes. Instead, narcissists put up a self-satisfied front that shatters every time something goes wrong.

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Their fragile ego explains why narcissists experience frequent and substantial fluctuations in self-esteem. If you get a bad grade on a test, or a poor performance review at work, your self-esteem probably takes a hit. "But for the narcissistic person even more so," says Edelstein, the Michigan psychologist. If something good happens, narcissists see it as confirmation of their brilliance. If something bad happens, they feel wrecked.

Indeed, individuals experience higher levels of narcissism after positive events, and lower levels of narcissism during times of stress. Moreover, mounting evidence that narcissists aren't all they thought they were is stressful. Perceived discrepancies between one's ideal self and one's actual self are associated with adjustment problems, lower self-esteem, and higher negative affect.

Narcissists may also experience more stress than non-narcissists due to their unique sensitivity to social stress. Edelstein's and other research suggests that narcissists have higher cortisol and cardiovascular reactivity in socially threatening situations, like when they're being watched or judged.

Why? Narcissism is generally defined and measured as using others to "satiate needs for admiration and recognition" and "self-enhance." Thus, by definition, narcissists rely on others to boost their fragile self-esteem—which means that each social interaction has high stakes. In her speech study, Edelstein thinks that the "experience of not getting a response from their audience was particularly stressful for [narcissists]." People who aren't narcissistic, by contrast, are less dependent on others for their self-worth, so they're less socially stressed.

Plus, narcissists' personalities make genuine social connection difficult, which can exacerbate stress. For example, narcissists have less grey matter volume in brain regions associated with emotional empathy. They're also defensive and untrusting. So the narcissist conundrum, as one researcher observed, is "their social behaviors ultimately end the relationships that they count on in order to maintain their grandiose self-views." Because people without good social support are particularly suceptible to stress, narcissists suffer worse from not only social stress but also life stress.

Still, the correlation between narcissism and cortisol persists even after controlling for perceived social support. Why else might narcissists be stressed? The final potential explanation—more of a personal theory—is that being stressed itself makes narcissists feel important, which reinforces both their stress and their grandiosity. If narcissists are to retain their inflated importance, everything that goes wrong must also be magnified on the same scale. Their stress serves to mask their true smallness. Even real tragedy must be extra-tragic: for example, survivors of traumatic events are more likely to develop PTSD if they're narcissistic.

Sustained stress could predispose narcissists to health problems like cancer, high blood pressure, coronary heart disease, diabetes, and strokes, Cheng says. For example, one study found that egocentric women showed hyperactivity of certain cardiovascular indicators that are linked to heart disease. And a longitudinal study by Edelstein suggests that hypersensitive narcissists develop more depressive symptoms, physical health problems, and lower life satisfaction in mid-life. Narcissists' stress—combined with their characteristic impulsivity, sensation seeking and invincibility complexes—may also instigate unhealthy coping in the form of substance abuse, aggressive driving, eating disorders or unsafe sex.

In the last three decades, American narcissism has risen by 30 percent. Over time, narcissism increases in people with high wellbeing and low emotional reactivity. As our nation's standard of living skyrockets and people acclimate to a shallower level of suffering, it's possible that our narcissism will increase along with, consequently, our stress and its side effects. Maybe this is nature's checks and balances: If we get too cocky, we'll begin to suffer toward humility.