In simple words, Prosopagnosia is an illness where the individual suffering from it cannot recognizes faces. The term Prosopagnosia comes from the Greek words for 'face' and 'lack of knowledge.'
It is also known as face blindness or facial agnosia. They are unable to recognize familiar people by just looking at their face and have to rely on other cues such as context, hairstyle, clothing to recognize someone. They do have trouble recognizing people once these cues have been changed, like meeting someone out of context or if they get a haircut.
Most people only have trouble recognizing faces, but sometimes the impairment even extends to objects, cars and animals. Many people have trouble with face processing. For example, they would not be able to judge someone's age or gender, emotional expression, or the direction of a person's gaze.
They also tend to have navigational difficulties. The other problem is that they have trouble following plots in movies or television shows as they cannot keep track of the characters. They also have trouble imagining the faces of the people they know.
This can affect people's lives in different ways. Some people have learned how to cope with it. They have found other ways to recognize people. Some people though have extreme difficulties cease of it. They end up avoiding social interactions and it creates problems in their interpersonal relationships and career. Some people even end up with social anxiety disorder in which they avoid and fear social situations.
It is a more common problem than people seem to think it is. It affects people in two different ways, some people get it after suffering neurological damage(acquired prosopagnosia) and some are born with (developmental prosopagnosia). There may be a genetic component to face prosopagnosia. Acquired prosopagnosia is very rare but developmental prosopagnosia is much more common. One 50 people may be suffering from this condition.
Acquired prosopagnosia occurs after a brain injury, stroke and onset of a degenerative disease. Developmental prosopagnosia occurs during childhood. It may be due to genetic factors or a prenatal brain damage or abnormality.
If you are wondering whether you are affected by this then as yourself these questions. Have you ever failed to recognize a close family member or friend, when you weren't expecting to see them? D you try to remember someone new by their hairstyle or a distinctive feature instead of their face? Do you confuse characters on television more than other people? Have there been times when you have failed to recognize your own self in the mirror or in pictures? Do you have problem recognizing people that wave at you on the street? Do you have difficulty recognizing someone after they have had a haircut? Do you have a hard time recognizing people if you see them out of context? If most of your answers were yes then you might be dealing with face prosopagnosia. It is better to get a doctor's opinion on the matter.