What Is Blood Type Personality?

Understanding the Japanese Concept of Ketsueki-gata

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Blood type personality is a Japanese concept called ketsueki-gata. This concept states that blood type shapes one’s temperament. Ketsueki-gata is considered a pseudoscience, a body of thought that appears to be based on scientific principles but is not actually rooted in fact.

Although there's no real proof that blood type influences personality, the belief is widespread in Japan and other Asian nations. It is also increasingly garnering interest in Western countries such as the United States.

Become more familiar with the theory of ketsueki-gata with this overview of its history, principles, influence in society, and potential pitfalls.

The History of Ketsueki-gata

In 1930, Japanese professor Tokeji Furukawa published a report in The Journal of Social Psychology called “A Study of Temperament and Blood-Groups.” In this paper, he argued that establishing a link between personality and blood type “might prove a useful basis for the objective study of temperament.”

He compared this effort to the ancient Greek physician Hippocrates’ classification of temperaments according to the four bodily “humors,” associated with bodily fluids: sanguine (blood), phlegmatic (phlegm), choleric (yellow bile), and melancholic (black bile).

While the idea behind humors was that four bodily fluids influence personality and behavior, Furukawa asserted that modern classifications of temperaments typically fell into two groups: physiological or psychological.

Blood Type Influences Personality Traits

The concept of blood type personality blends the two categories together, using physiology to explain the psyche.

Blood types A, B, O, and AB each have a unique effect on personality, Furukawa argued. Medically, the blood types are distinct from each other because of their antigens, molecules on the surface of red blood cells that spur the immune system to generate antibodies. But Furukawa’s interest in blood type went far beyond the scope of antigens.

In his paper, he included detailed charts to argue that blood type corresponds with temperament, but his research has been criticized for relying heavily on questionnaires and providing no empirical evidence.

Other researchers began to challenge Furukawa's claims about blood type personality just six years after he published his report. Still, the concept of ketsueki-gata never disappeared, as multiple books on blood personality type hit the shelves in the 1970s. Together, they drew attention to the subject once more.

Ketsueki-gata Research Outside of Japan

From 1984 to 1985, more than 200 publications printed papers on blood type personality, resulting in the enduring popularity of the concept in countries such as Japan, Korea, and Taiwan, and milder interest outside Asia. The American magazine Newsweek was one of the publications to explore the claims that blood type dictates personality.

“The Japanese have found a new way to ‘typecast’ people,” Newsweek declared in 1985. “It’s not astrology; it’s not studying the bumps on people’s heads. It’s blood typing. There is absolutely no scientific basis for typecasting by blood, of course, but that hasn’t stopped many Japanese from applying it to everything from love affairs to employment interviews."

Studies about ketsueki-gata have continued well into the 21st century all over the world, including Australia, Taiwan, and the United States. In 2021, a Tampa Bay, Florida, 12th grader named Tanu Bondu made headlines when her study on blood type personality was published in the International Journal of High School Research. “I used statistical analysis to see if there was a correlation,” she said. “I didn’t find any correlation, but I’m hoping to continue this research to expand it.”

So far, no rigorous scientific study including quantitative data has established a link between blood type and temperament. Yet, belief in ketsueki-gata persists—even in the United States, where authors have found success arguing that a person's blood type should inform lifestyle factors such as diet.

What Ketsueki-gata Believers Think About Personality  

Ketsueki-gata believers maintain that each of the four blood types corresponds with distinct personality traits, making different blood types more compatible with some than others. For example, here’s how the blood types purportedly break down by temperament: 

  • Type A: People with type A blood have been linked to positive traits such as creativity, cleverness, and cooperativeness, whereas their supposed negative traits include stubbornness and uptightness. Type A individuals are reportedly more common in Japan than people with other blood types.
  • Type B: Individuals with type B blood are supposed to be strong, passionate, empathetic, and decisive, but they have also been associated with selfishness and erratic behavior. People with this blood type are said to clash with those with type A blood.
  • Type AB: The purported strengths of those with type AB blood include rationality and adaptability, but their weaknesses are indecision, criticalness, and forgetfulness. This blood type is largely viewed as having the characteristics of both type A and type B individuals. Because this blood type is rare, the people who have it are heavily appreciated in Japan.
  • Type O: Type O people have been linked to characteristics such as confidence, determination, resilience, and intuition, but they are also supposedly self-centered and unstable. They are said to especially appear selfish to individuals with type A blood.

Meanwhile, in the U.S., blood type has not been linked to personality so much as it has been tied to specific diseases.

Type A individuals have been found to have an increased risk of stomach cancer and heart disease. Type B people also have an increased risk of heart disease and ovarian cancer. Type AB individuals have an increased risk of heart disease and preeclampsia in pregnant women. Type O individuals have an increased risk of ulcers and norovirus infections.

The Pitfalls of Blood Type Personality

Since blood type personality is widely accepted as reality in Japan, it does have some pitfalls. It has been linked to discrimination in both the workplace and in the singles scene. While positive and negative characteristics are associated with each blood type, some blood types are perceived to be better or worse than others.

Type B individuals, for example, are reportedly viewed as misfits in Japanese society because they’re said to go at their own pace and behave oddly. On the other hand, type AB individuals enjoy workplace advantages. In 1990, the Japanese newspaper Asahi Daily reported that Mitsubishi Electronics hired a team composed mostly of type AB people because of their purported knack for planning.

In the dating scene, someone might reject a potential partner purely based on fears of incompatibility due to blood type. Fortunately, the question “Ketsuekigata nāni?” (血液型なあに? What’s your blood type?) is typically asked in the very early stages of dating, so no one is likely to truly get their heartbroken over a purported blood type mismatch.

The Appeal of Blood Type Personality 

Although no legitimate scientific research linking blood type to personality has been published, people continue to believe in ketsueki-gata. Why? Psychologists have said that many simply enjoy the topic and use it as a way to break the ice with others. Moreover, in an uncertain world, the blood type personality theory can give people confidence about where they fit in and what their strengths and weaknesses are.

As with astrology, people often consult blood type personality because they believe it provides clues about their future. So, believers in ketsueki-gata aren’t primarily focused on what the science says about blood type personality, they’re largely focused on better understanding their own lives.

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