Prosopagnosia is a medical condition which is characterized by an inability to perceive faces. It is commonly known as “face blindness” — referring to an inability to remember faces, even those of people with whom one is familiar. Studies on prosopagnosia suggest that up to two percent of the population may be faceblind, and this estimate could be even higher with the assistance of better tracking and diagnostic tools. Currently, there is no known cure for prosopagnosia, although faceblind individuals can learn various tricks to help them get along socially.

The condition was first described and studied in detail in the 1940s, although it had been remarked upon much earlier. Initially, psychologists thought that the condition was caused only by trauma to the part of the brain which interprets information about the face, but over time people began to suspect that the condition could also be caused by genetic mutations. Prosopagnosia comes in varying degrees, with some patients not being able to perceive faces at all, while others have some facial recognition skills, or at least enough to learn the faces of familiar people.

It can be difficult for people without prosopagnosia to understand this condition. Faceblind individuals are perfectly capable of seeing faces, their brains just lack the necessary tools to process them. Since faces are used as identifiers and to provide social cues, prosopagnosia can be a serious social handicap for people who suffer from this condition. An individual with prosopagnosia may fail to recognize even close friends or family members by their faces, or subtle cues which come from facial expressions can be missed.

A person with face blindness tends to use other cues to gather information about people and their identities. Gait, haircut, clothing, and voice are all common identifiers which are used by the faceblind to figure out who people are. Sudden changes in someone's style or voice can be jarring, and can lead to missed identifications. In severe cases, for example, someone might fail to recognize his or her child at school after a change of clothes, which can be frustrating, embarrassing, and potentially dangerous as well.

Diagnosing prosopagnosia can be difficult, especially in a mild case. A patient might assume that everyone sees faces and processes information in the same way. Medical tests can be used to test brain function and to suggest a case of prosopagnosia, and the condition is also diagnosed through interviews with patients. Common complaints of the faceblind include difficulty following movie plots due to an inability to keep track of characters, and a common feeling of not being able to identify people, sometimes causing offense through unintended rudeness such as a failure to say hello to a friend.