Blood type personality tests became popular in Japan in the 1920s, but many people around the world and now interested in this possible objective way to look at their personality.

Personality typing goes back at least as far as the idea of the zodiac. Even when humans only had the stars and sky to go by, the urge to categorize different types of people was there. You could even make the argument that personality typing predates written language!

These days, you may look into your personality type by answering questionnaires or reading books on the subject. But there’s one popular personality typing system that’s completely based on your biology.

It’s called katsueki-gata, and it’s based on the theory that your blood type influences your behavior and personality.

There are eight basic blood types, and it is interesting to think about your personality being quite literally in your blood. From what we currently know, your blood type does tell a story about your family history and ethnic background.

As far as determining your personality, though, the evidence is just not there. Let’s take a look at what experts know and don’t know about this fascinating theory.

Beliefs about your blood type being connected to certain personality traits are nothing new. In Japanese culture, blood type has long been used as a basis for matchmaking and other predictions.

In the late 1920s, a research psychologist named Tokeji Furukawa added fuel to these cultural beliefs when he published a paper called “A Study of Temperament and Blood-Groups.”

For his study, Furukawa asked his subjects to assess their own personalities in an 11-question survey. He found that the answers to these questions did seem to correspond to participants’ blood types. The study wasn’t a big one, however, with 188 adult subjects between 27 and 70 years old and 425 younger subjects between ages 16 and 21.

Furukawa’s research used personality type categories first established by the ancient Greek physician Hippocrates:

  • sanguine
  • phlegmatic
  • choleric
  • melancholic

According to the results of these self-assessment surveys, it appeared that:

  • People with O blood types were phlegmatic (relaxed/peaceful).
  • People with A blood types were melancholic (self-reliant, deep thinkers).
  • People with B blood types were sanguine (outgoing and socially active).

In the grand scheme of things, this evidence was shaky, at best, but firmly took root in the cultural imagination of Japan and South Korea. Furukawa died in 1940, only 13 years after his initial paper on katsueki-gata was published and without providing further scientific proof for his theory.

In the 1970s, a Japanese journalist named Masahiko Nomi took Furukawa’s research a step further.

Nomi published a book called “Understanding Affinity by Blood Type” in 1971, and it became a runaway bestseller in Japan. In the book, Nomi posits that a quarter of a person’s behaviors and personality are the result of their blood type.

Nomi went on to publish more books offering advice and predictions for living based on blood type.

Despite a huge swell of interest in katsueki-gata, there continues to be no scientific evidence to make the case for it.

Certain blood types may be more resistant to certain health conditions or concerns, according to 2013 research. There’s even a prevailing belief that certain blood types do better with a blood-type specific diet.

But to date, no studies have found a correlation between blood type and personality in a large study group.

What we call your blood type is simply a way to talk about the antigens on the surface of your red blood cells. According to the ABO blood typing system, there are four main blood types:

  • A, which has the A antigen
  • B, which has the B antigen
  • AB, which has both A and B antigens
  • O, which has no antigen

Blood typing is essential for medical procedures, such as blood transfusions, to be performed safely. Since the ABO blood typing system was discovered in 1901, countless lives have been saved simply by having this information.

Even in the 2010s and today, books on the subject of katsueki-gata continue to top the bestseller lists in Japan. It’s certainly compelling to consider that your blood type reveals something about you, even if there’s no evidence to back it up. But why?

Personality typing based on something concrete, such as your blood type or the day you were born, can become even more appealing because they rest on something unchangeable about you.

As Furukawa noted in his original paper, “we have no objective method by which temperament can be judged or measured.” He hoped that blood typing, if it could be proven, would offer such an objective method.

We all have certain ideas about who we are and what is most important about us. But one of the most frustrating and limiting things about being human is that it’s impossible to know if our self-perception lines up with what other people see when they interact with us.

That makes the concept of personality typing in general so appealing: by answering a few simple questions, we think, we can reveal a deep truth about ourselves that we wouldn’t have been able to see otherwise.

What’s more, katsueki-gata claims to offer keys to how to approach romantic, workplace, and family relationships. It provides an explanation for your hardships.

Personality typing of any sort suggests that your social behaviors are mostly predetermined by something you cannot control, in addition to suggesting that your interactions with other personality types can be approached like a math equation with a solvable outcome.

It’s perfectly natural to want to find rules of order that can govern the way we understand relationships. As long as we understand the limitations within these systems, it’s not usually harmful to explore them.

If you’d like to talk with someone about your personality, therapy can be a great place to start. Learn more about how to find the right therapist for you here.

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There’s currently no scientific evidence to suggest that your blood type determines your personality. How could it? There are only four blood types, and your personality is layered, complicated, and completely unique to you.

However, there’s no harm in wondering whether certain tendencies or traits might be connected to certain blood types. Personality typing can be a fun way to try to understand yourself better, and can even give you language to explain the way you see yourself to other people.