Does blood type shape personality? How the idea spread from Japan

Does blood type shape personality?

No major scientific study has found a meaningful link between a person's ABO blood type and their personality. The belief that blood type shapes character, known in Japan as ketsueki-gata, began with a 1927 paper by the researcher Takeji Furukawa and turned into a nationwide phenomenon after a wave of popular books in the 1970s. It remains widely believed in Japan and South Korea today, appearing in hiring decisions, dating preferences and playground taunts, well past the point where psychological researchers consider the question closed.

Where the idea began

Takeji Furukawa published his thesis on ABO blood groups and behavior patterns in 1927, hypothesizing that people with type A blood tended to be gentle, shy and prone to worry, while people with type B blood were kinder and more cheerful. Scientific American later summarized his method as relying on questionnaires "but providing no controls or statistical tests," the kind of basic safeguard that lets other researchers check whether a pattern is real or a coincidence. The thesis drew attention in Japan but did not become a lasting mass movement until decades later.

How Nomi turned it into a phenomenon

In 1971, the journalist Masahiko Nomi, who had no medical or scientific background, published "Ketsuekigata de Wakaru Aisho" ("Understanding Your Love Compatibility Through Blood Type"), reviving Furukawa's decades-old hypothesis for a mass audience. Nomi went further than Furukawa had, at one point claiming a person's blood type could be read from body parts such as hair, teeth and organs. His books, and the imitators they inspired, turned ketsueki-gata into a full social phenomenon, with new titles on the subject peaking in 1983.

What the theory claims

As popularized in Japan and later in South Korea, the theory sorts people into four temperaments by ABO type. Furukawa's original hypothesis described type A people as gentle, shy and prone to worry, and type B people as kinder and more cheerful; the paperbacks that followed Nomi added equally specific, sometimes flattering and sometimes unflattering claims for type O and type AB. These are cultural stereotypes repeated in magazines, dating profiles and workplace small talk, not measurements, and no blood test can detect the traits the theory assigns to it.

What the studies found

The most thorough test came from Kengo Nawata of Kyoto Bunkyo University, who reanalyzed large-scale survey data in a 2014 paper in The Japanese Journal of Psychology. His datasets covered more than 10,000 people: two Japanese surveys from 2004 and 2005 with roughly 2,900 to 3,700 respondents each, and a 2004 United States survey of about 3,000 people. Across 68 personality measures, 65 showed no statistically significant difference between blood types, and even where a difference appeared, blood type accounted for less than 0.3 percent of the variation in personality, far too small to be meaningful.

Nawata's paper was not the first to reach that conclusion; a 2005 study of 2,681 Taiwanese college students using established personality measures likewise found no association. Belief has stayed high regardless: a 1986 survey found 96 percent of a sample of Japanese university students thought blood type influenced personality, and a 2002 survey of 1,102 Japanese adults put the figure at 75 percent.

Blood-type harassment in Japan and South Korea

The belief has had consequences beyond small talk. Japan has coined the term bura-hara, short for "blood-type harassment," for discrimination based on blood type: companies that factor blood type into hiring or job assignments, interviewers who ask about it directly and, in some cases, kindergartens that group children by blood type. A Japanese psychology professor has compared the practice to prejudice on any other trait, saying it "encourages people to judge others by the blood types, without trying to understand them as human beings."

South Korea has its own version. A Gallup Korea survey published in December 2017 found 58 percent of respondents believed blood type corresponds to personality, and type O was the most consistently favored group, ranking first in surveys from 2002, 2012 and 2017 alike. A 2013 survey found that 32 percent of women said they disliked dating men with type B blood, more than for any other type, and in 2004 a division of the Nonghyup agricultural cooperative drew public criticism for announcing it would only hire people with type O or type B blood.

How it is seen today

Real or Legend files the blood type personality theory as debunked. The largest and most careful surveys, covering more than 10,000 people across two countries, found no meaningful relationship between ABO blood type and personality traits, which is the core, testable claim the theory makes. Its continued popularity in Japan and South Korea is a cultural and media phenomenon, not evidence for it, and where it has shaped real decisions, in hiring, dating and classrooms, researchers and officials in both countries have pushed back against it as a basis for judging people.