What is the primary characteristic of Body Dysmorphic Disorder?

Body Dysmorphic Disorder (BDD) is primarily characterized by an obsession with perceived flaws in one's physical appearance. Individuals with BDD often experience a distorted self-image, leading them to fixate on minor or imagined defects that others may not even notice. This preoccupation can cause significant distress and impairment in social, occupational, or other important areas of functioning.

In contrast, the other choices do not align with the core features of BDD. Collecting items pertains to hoarding concerns, excessive focus on muscle size is indicative of another disorder known as muscle dysmorphia, and fears about losing personal possessions relate more closely to hoarding disorder or obsessive-compulsive disorder (OCD). Therefore, the obsession with perceived flaws in physical appearance stands out as the defining characteristic of Body Dysmorphic Disorder.