The researchers found that eyebrow distinctiveness, particularly qualities related to thickness and density, contributed to observers’ judgments. When distinctive eyebrows were transferred digitally to another person’s face, people’s impressions of that individual changed.

Why might eyebrows matter? Researchers suggested that eyebrows are important for facial recognition and can also be deliberately groomed. Because grandiose narcissism is associated with greater concern about appearance in some research, eyebrow grooming could potentially contribute to the effect.

However, this finding doesn’t mean thick eyebrows make someone a narcissist. It also doesn’t provide a reliable way to diagnose narcissistic personality disorder simply by looking at someone’s face. The study examined statistical associations and people’s ability to judge narcissistic traits across groups—not a foolproof test for individuals.

Narcissistic personality disorder is a clinical diagnosis involving a broader, persistent pattern of traits and behavior. Facial appearance alone cannot establish it. So while the eyebrow research makes an interesting psychology finding, someone’s behavior, relationships, and professionally assessed psychological patterns matter far more than the shape or thickness of their eyebrows.