How common is face blindness?

Face blindness, a mystifying condition that can trick us into believing we recognize people we've never met or make us fail to recognize those we have, has been previously estimated to affect between 2 and 2.5 percent of people in the world.

Now, a new study by researchers at Harvard Medical School (HMS) and the VA Boston Healthcare System is providing fresh insights into the disorder, suggesting it may be more common than currently believed.

Published in February 2023 in Cortex, the study findings indicate that as many as one in 33 people (3.08 percent) may meet the criteria for face blindness, or prosopagnosia. This translates to more than 10 million Americans, the research team said.

The study found similar face-matching performance between people diagnosed with prosopagnosia using stricter vs. looser criteria, suggesting that diagnostic criteria should be expanded to be more inclusive. That could lead to new diagnoses among millions who may have the disorder but don't realize it.

In the new study, led by Joseph DeGutis, HMS associate professor of psychiatry at VA Boston, the researchers found that face blindness lies on a spectrum -- one that can range in severity and presentation -- rather than representing a discrete group. The authors also provide diagnostic suggestions for identifying mild and major forms of prosopagnosia based on guidelines for major and mild neurocognitive disorders in the DSM5, the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders.

The study results are based on a web-based questionnaire and tests administered to 3,341 individuals. First, the researchers asked participants whether they experience difficulties recognizing faces in their everyday lives. Then they administered two objective tests to determine whether they had difficulties learning new faces or recognizing highly familiar, famous faces.

The results showed that 31 individuals out of the 3,341 had major prosopagnosia, while 72 of the 3,341 had a milder form. The researchers also observed that there were no neatly divided discrete groups of people with poor or good ability to recognize faces. Rather, the ability to recognize faces appeared to lie on a continuum, they said.

Finally, the researchers compared face-matching scores among people with prosopagnosia diagnosed using different criteria and found that using stricter diagnostic cutoffs did not correspond with lower face-matching scores.