You’ve heard of being cold-blooded, hot-blooded, red-blooded and blue-blooded – but is there really a blood type personality?

Despite popular belief, there is no solid scientific evidence to support the theory that blood type affects personality. A 2014 large-scale survey of over 10,000 people from both Japan and the US found that blood type does not influence personality at all. That doesn’t stop the theory from persisting, though.

Read on to find out more about the blood type personality theory, its history and the science behind it.

How does blood type personality work?

Blood type personality theory draws on the idea that your blood type can shape your personality, emotions and temperament. It is rooted in the scientific understanding of the four blood types - Type A, Type B, Type AB and Type O.

In Japan, the theory of blood type personality is called Ketsueki-gata.

  • Type A: According to Ketsueki-gata, people with Type A blood are believed to be earnest, creative and sensible but they can be stubborn and tense.
  • Type B: People with Type B blood are thought to be passionate, strong and active but they can also be selfish and irresponsible. 
  • Type AB: For Type AB, the characteristics are rational, cool and controlled while also being critical and indecisive.
  • Type O: Those who fall into the Type O blood group are believed to be confident, strong-willed, unpredictable and self-centred.

While the scientific basis for the existence of the four blood types is sound, the extent to which blood type influences personality is much less so. Approximately 40% of the variation in personality may be influenced by genetics. However, research - including a 2014 study of over 10,000 people in Japan and the US - has shown there is no evidence that the four blood types can determine an individual’s personality. 

As it stands, blood type personality has no solid scientific backing.

The history of blood type personality

While blood type personality theory is popular in Japan today, the history of the theory dates back thousands of years. Here’s a brief history of when and how it developed.

Ancient Greece and the four humors

The idea of personality traits inherited through blood dates back to the Ancient Greeks. Aristotle was one of the first scholars to write about the theory of blood type personality. Hippocrates also linked personality to the four bodily humors, four elements that he believed made up the human body and were responsible for health and illness. 

These four humours - sanguine, phlegmatic, choleric and melancholic - were believed to determine a person’s temperament and character.

The discovery of blood types

The four blood types as we know them today were discovered in 1900 by Austrian scientist Karl Landsteiner and his colleagues. Their work was instrumental in enabling successful blood transfusions, and in 1930 Landsteiner was awarded a Nobel Prize in Medicine for his work.

While the findings saved countless lives, Landsteiner’s discovery was co-opted by scientists to further theories on racial supremacy - the false idea that white Europeans were genetically superior to other races. After the First World War, pseudo-scientific theories based on blood type personality were used to further nationalist and colonialist agendas, using the four blood types as their starting point.

The work of Takeji Furukawa

In Japan, the theory of blood type personality gained immense popularity thanks to the work of Takeji Furukawa. Furukawa began studying blood type personality in the early 20th century, publishing his first paper on the topic in 1927.

Furukawa theorized that blood Types O and B were active. Their primary traits were labeled as aggressive, progressive and positive. In contrast, Types A and AB were passive, characterized by defensive, conservative and negative traits.

In 1930, Furukawa expanded his blood type personality theory, sorting each blood type into groups that corresponded with the Hippocratic humors:

  • Blood Type O - optimistic, sociable and strong-willed or phlegmatic
  • Blood Type A - shy, docile, worrying and impressionable or melancholic
  • Blood Type Bs - cheerful, sociable and frank or sanguine
  • Blood Type AB - this category of people were harder to judge and thought to have contradictory temperaments

Furukawa’s papers generated a large amount of interest in the idea of blood type personality in Japan and laid the foundation for theories that still exist today.

Furukawa’s legacy

Following the publishing of his research, Furukawa’s theories were scrutinised by G.N. Thompson Jr in 1936. Thompson argued that Furukawa’s studies into blood type personality were scientifically and methodologically flawed. After conducting his own research, Thompson found no relationship between blood type and personality or emotions.

After Furukawa’s death in 1940, the blood type personality theory fell out of favor but it was revived again in 1970 in Japan. Journalist Masahiko Nomi published a series of books on the topic that quickly became a huge hit. He sold millions of copies, cementing blood type personality theory into Japanese culture. The interest in blood type personality theory continues in Japan. In 2008, four books published on blood type personality reached the top 10 bestseller lists in Japan.

What evidence is there for blood type personality?

There has been a large amount of scientific research into blood type personality, but there is no concrete evidence that supports the theory.

One of the main problems is that much of the research done on blood type personality doesn’t list the number of people who were studied or surveyed. In many of the studies, the sample sizes for the different blood types aren’t equal, with fewer and sometimes zero blood Type B and Type AB individuals.

These problems in the methodology of the studies means that it’s impossible to draw a link between blood type and personality. The scientific evidence for blood type personality is flawed and in many cases it’s contradicting.

The truth about blood type personality

While genetics can have some influence on personality, there is no solid evidence for blood type personality theory. The idea that your blood type determines your core personality traits and characteristics is not backed by science but that hasn’t stopped it from becoming a hugely popular personality theory that’s still widely used today.

If you’re curious to learn more about personality theories, read this piece on the 16-type system for science-backed personality types.

Elizabeth Harris
Elizabeth is a freelance writer and ghostwriter. She’s an anthropologist at heart and loves using social theory to get deeper into the topics she writes about. Born in the UK, Elizabeth has lived in Copenhagen, Frankfurt and Dubai before moving most recently to Budapest, Hungary. She’s an ENTJ with ENFJ leanings. Find out more about her work at