The Japanese theory of ketsueki-gata seeks to explain personality traits via physiological factors, like blood type.

Blood donation bagsShare on Pinterest
Yaroslav Danylchenko/Stocksy United

Personalities are uniquely composed of many different components, such as your creativity, social tendencies, and temperament.

Our personalities are what make each of us individuals. But if you believe in blood type personality theory, you might think that you share those traits with other people of the same blood type.

For centuries, scores of people worldwide have looked to astrology to attribute certain personality traits to the planets and stars. Is the idea of a link between blood type and personality so far-fetched?

This concept is attributed to “ketsueki-gata,” a Japanese theory that first surfaced in the early 20th century. And while this idea remains unproven by the scientific community, the blood type personality theory helped pioneer research connecting psychology to physiology and biology.

Blood type personality theory is a Japanese concept formally known as ketsueki-gata. This concept suggests that your personality traits can be linked to one of the four blood types in the ABO Blood Grouping System.

According to the theory, the surface differences of blood cells in each blood type can create different biological responses that create your personality.

Blood type personality theory was first introduced in 1929 when professor Tokeji Furukawa published “A study of temperament and blood-groups.”

In his research, Furukawa linked personalities to different blood types.

Furukawa presented preliminary statistics for his theory based on small population samples. After publication, the evidence was later questioned due to possible political influences and the too-small sample size used in the research.

The theory of blood type personality persisted, however.

It was brought to the scientific community a second time in the 1970s by independent researcher and journalist Masahiko Nomi.

In his report “Understanding affinity through blood type,” Nomi expanded on Furukawa’s concepts. He included data from multiple method approaches, such as:

  • questionnaires
  • surveys
  • observation
  • statistical analysis

Nomi added to the original blood type personality theory and suggested that blood type could be linked to disease or physical predispositions.

And like Furukawa’s work, Nomi’s report also came under heavy scrutiny for being uncontrolled and anecdotal.

Despite this criticism, his outline for blood type personality theory remains the basis for current models. It was maintained and publicized by his son, Toshitaka Nomi, until Toshitaka died in 2006.

Since this concept’s emergence in Japan in the late 1920s, the blood type personality theory has been the subject of many studies worldwide.

Currently, no scientific evidence supports a cause-and-effect relationship between a person’s blood type and personality traits.

Even using current investigative methods, a 2021 study examining blood type and personality demonstrated no significant correlation.

Is there any link at all between personality and blood type?

Though most studies have shown that blood type doesn’t directly influence personality, some experts still believe there may be more to the story than what’s flowing through your veins.

In 2015, a study looked at personality through the lens of a relationship between blood type and genetics.

According to the study’s authors, certain blood types appeared to have a greater genetic probability of producing chemicals in the body that may influence impulsivity and sensation-seeking.

In this way, researchers suggest that blood type may be tied to personality.

However, this doesn’t mean that blood type is a “cause” of personality development.

For this reason, this study’s authors urged caution when interpreting the results as the personality link to blood type could be considered minimal at best.

Despite the controversial nature of the blood type personality theory, Furukawa’s concept remains a widespread belief with many worldwide.

The blood type personality theory uses the ABO Blood Grouping System. This standard system categorizes blood types into four groups:

  • blood type A
  • blood type B
  • blood type AB
  • blood type O

Your blood type is determined by the presence of antigens, or surface markers, on your cells.

These markers communicate with your immune system to keep you healthy. They let your body know which cells are yours, which ones are harmless, and which ones don’t belong there.

When any invading cell enters your body your system flags as foreign, your immune system may attack it if it doesn’t recognize the surface markers.

This is why someone with type A blood can’t receive a transfusion from someone with B blood type: The surface markers on the blood types are too different.

Not only do your surface antigens help with your body’s immune response, but blood type personality theory also suggests they’re responsible for the traits you express via your personality.

These traits may vary in significance from person to person and are often counteracted by opposing features.

Type O personalities, for example, are seen as kind-hearted, but they may also have moments where they come off as inconsiderate.

Blood type A personality traits

  • clever
  • loyal
  • sensitive
  • cooperative
  • organized
  • consistent
  • creative
  • stubborn
  • deliberate
  • reliable
  • trustworthy
  • nervous

Blood type B personality traits

  • passionate
  • carefree
  • decisive
  • empathetic
  • erratic
  • hyper-focused
  • go-getter
  • selfish
  • uncooperative
  • ambitious
  • outgoing
  • cheerful

Blood type AB personality traits

  • popular
  • caring
  • dependable
  • rational
  • indecisive
  • critical
  • self-centered
  • sociable
  • composed
  • forgetful

If you have type AB blood, the blood type personality theory indicates that you may have a mixture of the type A and type B groups.

Blood type O personality traits

  • confident
  • intuitive
  • outgoing
  • generous
  • kind
  • optimistic
  • jealous
  • insensitive
  • arrogant
  • unpredictable

In his original work, Furukawa sought to explain psychological processes through physiological ones.


Though no evidence definitively shows blood type may directly create your personality, the physical processes in your body can impact your thoughts, feelings, and behaviors.

A chemical imbalance, for example, could create mood fluctuations. Because your mood is often attributed to your personality, it’s easy to see how they might be tied together.

Blood type personality theory may not be supported by scientific research, but it does bring attention to how the body can impact the mind and vice versa.


However, the downside of theories with large followings but no empirical backing is that they can often impact people’s lives without cause.

In Japan, for example, the blood type personality theory is still widely accepted. People may base many major life decisions on blood type, such as:

  • marriages
  • jobs and career choice
  • political alignment
  • social circles and alliances

Furukawa’s blood type personality theory has even brought about a cultural practice in Japan known as “bura-hara,” which is blood type discrimination or harassment.

Though there’s currently no scientific proof backing the idea that your personality might be directly influenced by your blood type, some aspects of physical health might be tied to your blood type.

Research from 2021 suggests that as many as 49 diseases could be influenced by blood type — and in particular, linked to ABO blood type.

Blood type personality theory, also referred to as ketsueki-gata, is the belief that a person’s personality may be directly influenced by their blood type.

Much like astrology might attribute certain personality traits to movements in the cosmos, blood type personality theory attempts to connect a person’s characteristics to a physiological cause — blood type.

According to this idea, people who share a blood type may be similar in personality and characteristics. The theory looks at blood types A, B, AB, and O as predictors of innate traits.

For example, if you’re blood type B, you may be more likely to have a personality that’s a bit more erratic or outgoing.

This theory was pioneered by Japanese professor Tokeji Furukawa in 1929 but was found to be scientifically dubious.

The theory was later championed again in the 1970s by Japanese researcher and journalist Masahiko Nomi. Nevertheless, the blood type personality theory remained heavily scrutinized by the scientific community.

While there’s no scientific evidence that supports a direct link between blood type and personality, your behaviors, mood, and mental wellness may all be impacted by biological processes.

Blood type personality theory may be considered pseudoscience, but that doesn’t mean it can’t be used as a good conversation starter or to explore self-discovery.