What Is Prosopagnosia?

"Prosopagnosia" is also commonly called "face blindness." You can see the individual features of a face — eyes, nose, mouth — perfectly clearly, and your vision itself is fine. What becomes difficult is specifically taking in a face as a whole and working out whose face it is.

The severity varies widely. Some people struggle even with the faces of family and close friends, while others only have trouble recognizing someone they met once, after some time has passed. It's also common to rely heavily on cues other than the face — voice, hairstyle, gait, clothing — to tell people apart.

The word "prosopagnosia" is a coinage combining the Greek "prosopon" (face) and "agnosia" (not knowing, or an inability to recognize). Taken literally, it means something like "the state of being unable to know a face."

"Agnosia" is a medical term describing a broad category of conditions where a sense itself works fine, but the person can't recognize what it's perceiving. Prosopagnosia can be thought of as the type of agnosia limited specifically to faces — a different mechanism entirely from simply not being able to see a face clearly due to poor vision.

The word "prosopagnosia" is generally traced back to a 1947 case report by the German neurologist Joachim Bodamer. He described a patient who, after a head injury, lost an ability to identify faces that had previously been completely normal, and coined the term "prosopagnosia" to describe it.

After this report, the idea that face identification alone could be selectively impaired — and that it seemed to relate to specific brain function — gradually became a subject of research. That said, similar symptoms are believed to have been recorded sporadically even before this.

Prosopagnosia is broadly divided into two types: acquired and developmental. Acquired prosopagnosia occurs when someone who previously identified faces without any problem develops difficulty following a stroke, head injury, or brain illness. It's thought to involve a region of the brain that includes the fusiform gyrus in the temporal lobe — an area on the inner surface of the brain, roughly below the ears, believed to play a major role in processing faces.

Developmental prosopagnosia, by contrast, is a lifelong difficulty with face identification present since early childhood, without any clear triggering illness or injury. Because it feels like "normal" to the person experiencing it, many people don't realize their difficulty with faces is unusual until adulthood. Both types vary in severity and in which situations cause difficulty from person to person, and neither can be diagnosed by a single uniform standard.