Prosopagnosia, also known as face blindness, means you cannot recognise people's faces.
Face blindness often affects people from birth and is usually a problem a person has for most or all of their life. It can have a severe impact on everyday life.
Many people with prosopagnosia are not able to recognise family members, partners or friends.
They may cope by using alternative strategies to recognise people, such as remembering the way they walk or their hairstyle, voice or clothing.
But these types of strategies do not always work – for example, when a person with prosopagnosia meets someone in an unfamiliar location.
A person with prosopagnosia may avoid social interaction and develop social anxiety disorder, an overwhelming fear of social situations.
They may also have difficulty forming relationships or experience problems with their career. Feelings of depression are common.
Some people with prosopagnosia cannot recognise certain facial expressions, judge a person's age or gender, or follow a person's gaze.
Others may not even recognise their own face in the mirror or in photos.
Prosopagnosia can affect a person's ability to recognise objects, such as places or cars.
Many people also have difficulty navigating. This can involve an inability to process angles or distance, or problems remembering places and landmarks.
Following the plot of films or television programmes can be almost impossible for someone with prosopagnosia because they struggle to recognise the characters.
Someone with prosopagnosia may worry that they appear rude or not interested when they fail to recognise a person.
There are 2 types of prosopagnosia:
In the past, most cases of prosopagnosia were thought to occur after a brain injury (acquired prosopagnosia).
But research has found that many more people have prosopagnosia without having brain damage (developmental prosopagnosia) than was first thought.
Several studies have indicated that as many as 1 in 50 people may have developmental prosopagnosia, which equates to about 1.5 million people in the UK.
Most people with developmental prosopagnosia simply fail to develop the ability to recognise faces.
Someone born with the condition may not realise they have a problem.
Developmental prosopagnosia may have a genetic component and run in families.
Many people with the condition have reported at least 1 first-degree relative, such as a parent or sibling (brother or sister), who also has problems recognising faces.
Acquired prosopagnosia is rare. When someone acquires prosopagnosia after a brain injury, they'll quickly notice that they have lost the ability to recognise people they know.
But if prosopagnosia 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're not able to recognise faces as well as other people can.
Prosopagnosia is not related to memory problems, vision loss or learning disabilities, but it's sometimes associated with other developmental disorders, such as autism spectrum disorder, Turner syndrome and Williams syndrome.
If you have problems recognising faces, your GP may refer you to a clinical neuropsychologist working within the NHS or private practice.
You may also be referred to a researcher who specialises in the field and is based at a nearby university.
You'll have an assessment involving a range of tests that assess your face recognition ability, among other skills.
For example, you may be asked to:
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 programme.
There's no specific treatment for prosopagnosia, but researchers are continuing to investigate what causes the condition, and training programmes are being developed to help improve facial recognition.
It's thought that compensatory strategies that help with person recognition, or techniques that attempt to restore normal face-processing mechanisms, may work for some people with either developmental or acquired prosopagnosia.
A person's age when their brain was damaged (in the case of acquired prosopagnosia), the type and severity of the brain injury, and the timing of treatment are all thought to be important factors in how effective a rehabilitation programme will be.
Many people with prosopagnosia develop compensatory strategies to help them recognise people, such as recognising a person's voice, clothing or the way they walk.
But compensatory strategies based on contextual cues do not always work, and may break down when a person with prosopagnosia meets someone they know in an unexpected location or who's changed their appearance.
The charity has a factsheet with some useful information about living with the condition, including social, observational, memory and navigation strategies, plus tips for watching TV and films.
It can be difficult to recognise prosopagnosia in children, but the following are potential signs:
The Centre for Face Processing Disorders, based at Bournemouth University, has more information about prosopagnosia in children.