You wave at a stranger you mistook for a friend. You fail to recognize a colleague at the supermarket. A film loses you because the characters all look alike. For most people these are occasional slips. For people with prosopagnosia, face blindness, they are daily life.
What prosopagnosia is
Prosopagnosia is a specific difficulty recognizing faces, not a memory problem, not low intelligence, and not a lack of interest in people. The developmental form is present from childhood without any brain injury, and research suggests around 2% of people experience it, most without ever having a name for it. Many build elaborate workarounds without realizing it: recognizing people by hair, voice, gait, glasses or context, and quietly panicking when someone changes their hairstyle or appears somewhere unexpected.
The signs people report
The most common experiences, drawn from the research literature: mistaking known people for strangers, struggling when someone changes hairstyle or wears a hat, losing track of film characters, confusing family members at gatherings, failing to recognize people out of their usual context, and warning new acquaintances that you are "bad with faces". Many people also report social anxiety built on years of accidentally snubbing people.
How researchers screen for it
In 2015, Shah and colleagues published the 20-item Prosopagnosia Index (PI20) in Royal Society Open Science, a validated self-report questionnaire that has become a standard research screening tool worldwide. Twenty statements, a 1-to-5 agreement scale, a score from 20 to 100. Their published guidance: scores of 65 or more are suggestive of developmental prosopagnosia, with 65-74 broadly mild, 75-84 moderate and 85-100 severe. The authors released it under an open license, which is why we can offer it in full.
Take it here
We have added the complete, unmodified PI20 to our test library, free, in six languages, with your score and its published interpretation in about 5 minutes: take the face blindness test (PI20).
What a high score means, and does not mean
The PI20 is a screening questionnaire: a high score means your self-reported experiences resemble those of people formally identified with prosopagnosia, and that a conversation with a neuropsychologist, who can run objective tests like the Cambridge Face Memory Test, would be reasonable. It is not a diagnosis. Also worth knowing: face recognition difficulties are reported more often among autistic people, though prosopagnosia frequently occurs entirely on its own. If faces are only one part of a broader pattern for you, our autism screening may also be informative.
Source: Shah, P., Gaule, A., Sowden, S., Bird, G. and Cook, R., "The 20-item prosopagnosia index (PI20): a self-report instrument for identifying developmental prosopagnosia," Royal Society Open Science 2:140343 (2015), CC-BY. Educational summary, not a diagnosis or medical advice.