Tests showed that men performed worse after they were shown pictures of fair-haired women, reports the Daily Telegraph.
Researchers concluded that rather than simply being distracted, the men were subconsciously copying the stereotype of the "blonde bimbo".
Academics at the University of Paris X-Nanterre examined men's ability to complete general knowledge tests after exposure to women with different hair colours.
Throughout both trials, those participants exposed to blondes recorded the lowest scores.
"This proves that people confronted with stereotypes generally behave in line with them," said Thierry Meyer, joint author of the study and professor of social psychology at the university.
"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."