Quirky Japan Chronicles – Episode 19: Blood Types and Personality — Japan’s Favourite Pseudoscience
By Yoshi | Japan Unveiled
I have a colleague — a perfectly intelligent, thoroughly educated, professionally successful woman in her early forties — who, upon meeting someone new, asks their blood type within the first fifteen minutes of conversation.
Not as a medical inquiry. As an assessment.
She is, she will tell you, a Type A herself. This explains — she will explain — her perfectionism, her attention to detail, her occasional difficulty with spontaneity. The new colleague who has just revealed themselves to be a Type B is being unconsciously evaluated: Type Bs are, in this framework, creative and individualistic but sometimes selfish and irresponsible. The Type O is reliable and practical but occasionally stubborn. The Type AB is complex, thoughtful, and possibly a little difficult to read.
None of this is supported by any credible scientific research. Every serious study that has examined the proposed relationship between ABO blood type and personality has found no statistically significant correlation. The scientific verdict is clear and has been clear for decades.
My colleague knows this. She has been told this. She continues to ask about blood types within fifteen minutes of meeting people, because — she says, with complete self-awareness — she can’t help it. She grew up with this. It’s in her thinking now.
This is ketsueki-gata (血液型) — Japan’s blood type personality system — and it is one of the most widely held beliefs in Japanese popular culture, one of the most frequently discussed topics in Japanese social interaction, and one of the most thoroughly debunked pseudosciences in the scientific literature.
It is also genuinely fascinating.
What the System Says
The ABO blood type system — developed in 1901 by Karl Landsteiner, for which he received the Nobel Prize in 1930 — categorises human blood into four types (A, B, O, and AB) based on the presence or absence of specific antigens on red blood cells. The system was developed entirely for medical purposes: determining blood type compatibility for transfusions.
The Japanese blood type personality system has taken these four medical categories and assigned to each a distinct personality profile:
Type A — organised, responsible, patient, and conscientious. Sensitive to others’ feelings, anxious about making mistakes, occasionally rigid and overly cautious. Prone to stress and difficulty delegating. The perfectionist type, associated with Japanese virtues of conscientiousness and care for others.
Type B — creative, passionate, individualistic, and optimistic. Spontaneous, self-centred by others’ assessment, occasionally unreliable because they follow their own enthusiasm rather than social obligation. The free spirit type, and — it must be said — the personality category that carries the most social stigma within the ketsueki-gata framework.
Type O — confident, practical, competitive, and socially skilled. Natural leaders who are direct and decisive. Occasionally insensitive and hot-headed. The achiever type, associated with leadership qualities.
Type AB — rational, creative, diplomatic, and detached. Capable of seeing multiple perspectives, occasionally cold or indecisive. The enigmatic type, associated with intellectual sophistication.
The distribution of blood types in Japan: approximately 38% Type A, 27% Type O, 22% Type B, 13% Type AB. This is reasonably close to the global distribution, though with a slightly higher proportion of Type A than the global average.
The History: Where This Came From
The connection between blood type and personality did not originate in Japan. It originated in a 1927 paper by Takeji Furukawa, a Japanese educator who proposed the theory — without substantial evidence — as a mechanism for explaining personality differences. The theory attracted some interest but did not initially take widespread hold.
The idea was revived and popularised in the 1970s primarily through a 1971 book by Masahiko Nomi — Understanding Affinity by Blood Type — and subsequent works by Nomi and his son Toshitaka. The Nomis were prolific writers and effective popularisers who produced a large body of books on blood type personality that sold in large numbers through the 1970s and 1980s.
The popularisation of ketsueki-gata through the Nomi books coincided with a specific period in Japanese popular culture — the era of personality tests and fortune-telling that flourished in women’s magazines and general interest publishing. Blood type personality fit naturally into this cultural moment: accessible, memorable, social (you can discuss blood types with anyone who knows theirs), and providing the specific pleasure of a framework for understanding yourself and others.
The system became embedded in Japanese popular culture through repetition across media — women’s magazines, television programming, dating guides, management books — until it achieved the specific status of a belief that people hold not because they have consciously evaluated and accepted it, but because it has been part of the cultural air for so long that it simply is, assumed rather than chosen.
How Deeply It Goes: The Social Reality
The depth of blood type belief in Japan is not merely a matter of casual conversation. It has genuine social consequences.
Discrimination: burahara. The term burahara — a contraction of blood type harassment — has entered common usage to describe the specific social and professional discrimination that can result from blood type assumptions. The Type B person who faces assumptions of selfishness and unreliability in professional contexts; the Type AB person who is treated as eccentric or difficult; the hiring manager who uses blood type as an unofficial screening criterion — these are real phenomena in Japan, documented by researchers and acknowledged by organisations including the government’s Ministry of Health, Labour and Welfare, which has issued guidance on blood type discrimination in hiring.
Relationships: compatibility and incompatibility. Blood type compatibility is a significant factor in Japanese dating culture — whether two people’s blood types are compatible (in the specific framework of ketsueki-gata compatibility charts) is a question that is taken seriously by a significant portion of people seeking romantic partners. Specific type combinations are considered particularly compatible or particularly fraught: the Type A and Type O pairing is generally considered compatible; the Type A and Type B pairing is considered the most difficult.
Consumer products. The ketsueki-gata market is substantial. Books on blood type personality remain consistent bestsellers. Blood type-specific products — stationery, accessories, health supplements — are regularly introduced and find buyers. A notable example from the early 2000s: Mitsubishi Pencil produced blood type-specific pencils for school examinations, marketed with the logic that the specific pencil suited to each blood type would help the student perform optimally.
Jikoshoukai (self-introduction). In Japanese professional and social contexts where people introduce themselves to a group — the jikoshoukai is a standard element of the first meeting in most Japanese professional environments — blood type is sometimes included alongside name, workplace, and hometown as a basic piece of self-identification. Not universally, and the practice has been declining among younger generations in urban areas, but its persistence in even a significant minority of introductions indicates how deeply the framework is embedded.
The Science: Why It’s Wrong
I want to be direct about this because I think it deserves directness: there is no credible scientific evidence that ABO blood type has any causal relationship with personality traits.
The studies are extensive. The methodology has improved significantly over the decades as better tools for personality measurement and larger sample sizes have become available. The results are consistent: when blood type and personality are rigorously measured in properly controlled studies, no statistically significant relationship appears.
The 2014 study published in PLOS ONE — using data from approximately 10,000 participants in Japan and 1,800 in the United States — found no correlation between blood type and the fourteen personality dimensions measured. The authors noted that the consistency of the null result across studies and cultures strongly suggested that no real relationship exists.
The mechanism by which blood type could affect personality is also biologically implausible. The ABO blood type system affects the antigens present on red blood cells and certain other tissues. The causal path from red cell antigens to personality is not established and has not been plausibly proposed.
The persistence of the belief despite this scientific consensus is itself a fascinating phenomenon — and it is a phenomenon with a specific explanation that does not require assuming that Japanese people are less rational than others.
Why It Persists: The Psychology of Useful Frameworks
The blood type personality system persists because it provides something genuinely useful to the people who use it, independent of its accuracy.
The categorisation need. Human beings are powerfully motivated to categorise other people — to have frameworks that allow rapid assessment of social situations, of whether a new person is likely to be compatible, of what to expect from different types of interaction. This motivation is not irrational — it is a cognitive efficiency system in environments where rapid social assessment has historically mattered. The blood type system provides a four-category framework that can be applied to anyone and that generates expectations about interaction.
The confirmation bias mechanism. Once a person has a blood type framework and applies it consistently, they will remember the instances where the framework seemed to predict correctly and forget or reinterpret the instances where it predicted incorrectly. This is confirmation bias — the universal human tendency to weight evidence that confirms existing beliefs more heavily than evidence that disconfirms them. A Type B person who is occasionally selfish confirms the framework; a Type B person who is consistently conscientious is an exception that does not invalidate the general pattern.
The Barnum effect. The personality descriptions associated with each blood type are written broadly enough to apply to most people in most circumstances. The Type A description of perfectionism and sensitivity to others’ feelings describes a large proportion of the general population; most people who read it will find aspects of themselves in it. This is the Barnum effect — the tendency to accept vague, general personality descriptions as accurate descriptions of oneself — applied to a four-category system.
The social function. Discussing blood types is a specific, low-stakes form of social interaction — a topic that is personal enough to be interesting, light enough not to be threatening, and universal enough (everyone has a blood type) that it can be used with strangers as easily as with acquaintances. Blood type conversation is social lubricant — and the value of social lubricant is independent of the accuracy of its content.
The International Comparison: Korea and Taiwan
Japan is not alone in its blood type personality culture. South Korea and Taiwan have developed similar blood type personality frameworks, probably through Japanese cultural influence during the colonial period and the subsequent spread of Japanese popular culture through the region.
In South Korea, blood type personality (hyeoraekhyeong) is as deeply embedded as in Japan, with the same social consequences — burahara-equivalent discrimination, blood type in dating profiles, blood type consumer products. The Korean Wave entertainment industry has produced numerous references to blood type personality, which has contributed to its international spread to other countries with significant Korean cultural influence.
The specifically East Asian prevalence of blood type personality belief — in contrast to the negligible role it plays in European, North American, and most other Asian cultures — is itself worth examining. It suggests that the cultural conditions that made blood type personality believable and useful are specific to this cultural context: perhaps the particular combination of the framework’s appearance in a period of social change, the specific media environment of Japan in the 1970s and 1980s, and the specific social functions the framework served in Japanese group-oriented social culture.
How to Handle the Question
For foreign visitors to Japan who are asked about their blood type — which will happen, particularly in social contexts with Japanese people of the generations that take ketsueki-gata most seriously — a few practical observations.
You do not know your blood type: a perfectly acceptable response. Many people, particularly in countries where blood typing is not routinely performed, simply do not know their type. This is received without judgment.
You know your type and find the question charming: engage with it. Ask about your type’s characteristics. Compare them humorously with your actual personality. This is the social game being offered and it can be genuinely enjoyable.
You know your type and find the question mildly frustrating: you can say so, gently. “In my country we don’t really believe blood type affects personality” is a culturally informative response that most Japanese people will receive with interest rather than offense.
What I would caution against: the sharp, immediate correction — “that’s pseudoscience” — delivered to someone who is using blood type conversation as a social gesture rather than a scientific claim. The social context is the thing being offered, not the belief system. Treating the social gesture as a scientific claim to be refuted is the specific kind of social mistake that makes cross-cultural interaction more difficult than it needs to be.
Be Type O about it: confident, practical, socially skilled.
Even if you’re not.
— Yoshi 🩸 Central Japan, 2026
Enjoyed this? You might also like: “Quirky Japan Chronicles – Episode 11: Sleeping at Work Is Encouraged” and “Why Japanese People Work So Much — and Whether They Actually Want To” — both available on Japan Unveiled.
