Body dysmorphic disorder (BDD), also known in some contexts as dysmorphophobia, is a mental disorder defined by an overwhelming preoccupation with a perceived flaw in one's physical appearance. In BDD's delusional variant, the flaw is imagined. When an actual visible difference exists, its importance is disproportionately magnified in the mind of the individual. Whether the physical issue is real or imagined, ruminations concerning this perceived defect become pervasive and intrusive, consuming substantial mental bandwidth for extended periods each day. This excessive preoccupation not only induces severe emotional distress but also disrupts daily functioning and activities. The DSM-5 places BDD within the obsessive–compulsive spectrum, distinguishing it from disorders such as anorexia nervosa.

BDD is estimated to affect from 0.7% to 2.4% of the population. It usually starts during adolescence and affects both men and women. The BDD subtype muscle dysmorphia, perceiving the body as too small, affects mostly males. In addition to thinking about it, the sufferer typically checks and compares the perceived flaw repetitively and can adopt unusual routines to avoid social contact that exposes it. Fearing the stigma of vanity, they usually hide this preoccupation. Commonly overlooked even by psychiatrists, BDD has been underdiagnosed. As the disorder severely impairs quality of life due to educational and occupational dysfunction and social isolation, those experiencing BDD tend to have high rates of suicidal thoughts and may attempt suicide.