Blood Type and Personality: What the Evidence Shows

The four-type personality framework

In the Japanese ketsueki-gata or blood type personality system, each of the four ABO types is associated with a cluster of traits. The descriptions vary across books and magazines but the broad outlines are consistent enough to be recognisable.

Type A is described as serious, organised, considerate, and anxious. Type B is described as creative, passionate, individualistic, and (in less flattering versions) unreliable or selfish. Type O is described as confident, leader-like, optimistic, and competitive. Type AB is described as rational, eccentric, dual-natured, and unpredictable.

Compatibility lore extends the framework into relationships: type O and type A are said to make a stable couple, type B and type AB are said to be challenging together, and so on. None of these claims have a peer-reviewed evidence base.

Origin: Tokeji Furukawa, 1927

The modern Japanese version traces to Tokeji Furukawa, a teacher who published a 1927 paper in the Japanese journal Psychological Research proposing a link between ABO type and temperament. Furukawa drew on small samples and unsystematic observation. The idea was picked up by the Imperial Japanese Army in the 1930s, who briefly considered using blood type to organise units, before the practice was abandoned.

The idea re-entered popular culture through Masahiko Nomi's 1970s self-help books, which sold widely and reframed the framework as a guide to relationships, careers, and self-understanding. His son Toshitaka Nomi continues to publish in this vein. The framework has been a recurring topic in Japanese magazines, television, and popular psychology since.

The cultural reach is substantial. A 2012 BBC report on ketsueki-gata noted that Japanese politicians sometimes disclose their blood type in profiles, that several Japanese morning shows include daily blood-type horoscopes, and that workplace and school discrimination based on blood type (bura-hara, blood-type harassment) is a recognised concern.

The published tests

The strongest empirical test to date was published in PLOS ONE in 2015 by Cho et al., who used a sample of 2,547 Japanese adults and 7,272 American adults, applying standard personality inventories (the Big Five) and looking for the predicted ABO-by-trait correlations. The result: no effects survived correction for multiple comparisons. The personality differences predicted by the cultural framework were not present in the data.

Earlier work by Wu, Lindsted, and Lee (2005) applied the Eysenck Personality Questionnaire to 2,681 Taiwanese university students and similarly found no associations between ABO type and personality scores beyond chance. Sakamoto and Yamazaki's 2004 paper in Personality and Individual Differences noted that the published positive findings in Japanese-language journals tended to be small, methodologically weak, and unreplicated, consistent with the file-drawer problem.

The pattern is the same across the two decades of empirical work: when the effect is tested with adequate sample size and standard personality inventories, it disappears.

Why the belief feels accurate

Two well-documented psychological effects produce the experience of accuracy. The first is the Barnum effect, named after the showman P. T. Barnum and demonstrated in a 1949 paper by Bertram Forer. Forer gave students a personality description he claimed was based on individual analysis. The descriptions were identical and assembled from horoscopes. Students rated the accuracy at 4.3 out of 5. Vague, general personality descriptions feel personally accurate to almost anyone.

The second is confirmation bias. When you know that your colleague is type B and the framework predicts type-B people are creative, you remember the times your colleague did something creative and forget the routine, conventional days. Across hundreds of small interactions, the matches accumulate in memory and the mismatches do not.

Astrology, the Myers-Briggs Type Indicator, and the Enneagram all rely on similar psychological mechanisms. The frameworks feel useful, generate conversation and self-reflection, and do no harm in casual contexts. They become problematic when they are used in hiring, dating, or other high-stakes decisions.

Bura-hara: blood-type harassment

Within Japan, the cultural belief has produced a recognised form of discrimination. People with type B (described as selfish in some versions of the framework) and type AB (described as eccentric or unpredictable) report being passed over for jobs or relationship opportunities because of their blood type. The phenomenon is called bura-hara, short for blood-type harassment, and the Japanese ministry of health, labour and welfare has periodically warned employers against using ABO information in hiring decisions.

Mass-market kindergartens in Japan have at times grouped children by blood type for social-skills training, with type-B children placed in different groups from type-A children. The practice has been criticised by Japanese paediatricians and educators as introducing self-fulfilling labels with no basis in evidence.

Cultural beliefs that label children by an immutable trait create real consequences regardless of whether the belief is true. The same dynamic operates in any cultural context where a trait is treated as predictive of behaviour without supporting evidence.

Cultural reach beyond Japan

The belief is mainstream in Japan, South Korea, and Taiwan. Korean dating apps sometimes feature blood type as a profile field. K-pop fan communities pay attention to members' blood types. South Korean popular media regularly features blood-type-themed dramas and films, including the 2005 film My Boyfriend Is Type B, which built a romantic comedy around the cultural assumption that type-B men make difficult partners.

The reach is much weaker in Europe, the Americas, and most of Africa. Western popular culture treats blood type and personality as an exotic curiosity rather than a working framework. Many Western adults do not know their blood type at all, which limits the framework's practical use as a social shortcut.

China has its own variant, with broader cultural attention to blood type as a social signal but less systematic personality theory than the Japanese version. See our Japan blood type page for population-level distribution data.

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