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.
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 doctor to a clinical neuropsychologist working within the NHS 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, 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.