Prosopagnosia, also known as "face blindness", is the inability to recognise faces – a problem that usually affects the person for most or all of their life.
Many people with prosopagnosia cannot even recognise family members, partners or friends.
They may cope by using alternative ways to recognise people, such as remembering the way they walk, or their hairstyle, voice or clothing.
However, compensation strategies like this don't always work, and the condition can have a severe impact on a person's everyday life.
What impact can it have?
Some people with prosopagnosia may avoid social situations and develop social anxiety disorder. Relationships and careers can be affected.
Some are also unable to recognise facial expressions, follow a person's gaze or judge a person's age or gender.
Prosopagnosia can also affect a person's ability to recognise other objects, such as places or cars.
Some may not even recognise their own face in the mirror or in photos.
Following the plot of television programmes and movies can be almost impossible, because characters aren't recognisable.
Even those who cope well with prosopagnosia may worry that they seem rude or disinterested when they fail to recognise a person.
What is the cause?
Most people with prosopagnosia simply fail to develop the ability to recognise faces, despite not having any brain damage.
They may have been born with this condition, so may not realise they have the problem.
There may be a genetic influence in developmental prosopagnosia, as it has been shown to run in families.
Less commonly, prosopagnosia can be caused by brain damage following a severe head injury, stroke or brain disease, including dementia.
When prosopagnosia is acquired in this way, the person will quickly notice that they have lost the ability to recognise people they know.
However, if it occurs after brain damage in early childhood, before the child has fully developed the ability to recognise faces, they may grow up not realising they are unable to recognise faces as well as other people can.
Prosopagnosia is not related to memory problems, loss of vision or learning disabilities, although it is sometimes seen in people with autistic spectrum disorders.
How common is it?
According to the Centre for Face Processing Disorders at Bournemouth University, acquired prosopagnosia is rare. However, developmental prosopagnosia appears to be much more common – affecting up to 1 in 50 (the equivalent of about 1.5 million people in the UK).
How is it diagnosed?
People with face recognition difficulties may be referred by their GP to a clinical neuropsychologist working within the or private practice.
Alternatively, they may be referred to a researcher who specialises in the field and is based at a nearby university.
They will have an assessment involving a range of tests that assess their face recognition ability, among other skills. They may be asked to:
memorise and later recognise a set of faces they have never seen before
recognise very famous faces
spot similarities and differences between faces that are presented next to each other
judge age, gender or emotional expression from a set of faces
If you live within travelling distance of Bournemouth University, the Centre for Face Processing Disorders may be able to offer you a formal testing session and the opportunity to take part in their research.
Can it be treated?
There's no specific treatment for prosopagnosia, although researchers are investigating the cause and working on training programmes designed to help improve facial recognition.
Treatment may focus on the development of compensatory strategies (clues that can be used to recognise people) or attempt to restore more typical face recognition strategies.
Headway has a long list of tips and coping strategies (PDF, 405kb), which have been suggested by people with prosopagnosia. It covers social, observational, memory, preparation and navigation strategies, as well as tips for watching films and TV shows.
More information and support
Headway: face blindness research
Prosopagnosia Research at Bournemouth University
Headway: prosopagnosia factsheet (PDF, 405kb)
Friends and family may seem like strangers to someone with prosopagnosia
Does my child have it?
It can be difficult to spot prosopagnosia in children, but the following are potential signs:
your child frequently fails to recognise familiar people when encountering them unexpectedly
they are particularly clingy when in public places
they wait for you to wave when you're collecting them from school, or approach strangers thinking they are you
they are socially withdrawn at school and have difficulty making friends (this may be in contrast to more confident behaviour at home, when recognition is not an issue)
they find it difficult to follow plots of films or TV shows
Source: Centre for Face Processing Disorders