The study, conducted by Thierry Meyer, professor of social psychology at the University of Paris X-Nanterre and team, found that men's mental performance drop, apparently because they believe they are dealing with someone less intelligent when they come across blonde women.
In the two-trials based study, researchers discovered what might be called the "bimbo delusion" by studying men's ability to complete general knowledge tests after exposure to different women.
The analysis found that all the participants exposed to images of blondes recorded the lowest scores in academic tests.
Furthermore analysis convinced the team that, rather than simply being distracted by the flaxen hair, those who performed poorly had been unconsciously driven by social stereotypes to "think blonde".
"This proves that people confronted with stereotypes generally behave in line with them," Times Online quoted Meyer, as saying.
"In this case blondes have the potential to make people act in a dumber way, because they mimic the unconscious stereotype of the dumb blonde," Meyer added.
The finding suggests that people's behaviour is powerfully influenced by stereotypes.
The study is published in the Journal of Experimental Psychology.