In Japan, there is a belief that a person’s personality is linked to their blood type. This may sound strange, but the idea is not too dissimilar to astrology’s popularity in the UK or the US today. However, Ketsueki-gata, as it is called, is unique and has deep cultural roots in Japan’s recent history. While it may seem trivial to us, in Japan a person’s blood type has important implications for how they are understood as an individual and how they may perform in their jobs. So what’s going on here?

What does your blood type say about you?

Okay, let’s get the fun part out of the way first. For the curious out there, this is what Ketsueki-gata says about the different blood types.

Type A blood: According to a casual internet search, people with Type A blood are regarded as warm, friendly, and compassionate. However, they can be obsessive, stubborn, and uptight. Type A individuals are said to be more common in Japan that people with other blood types.

Type B blood: Individuals with Type B blood are thought to be strong, passionate, decisive, and empathetic, but they are also more selfish, erratic, unforgiving, and wild. People with this type of blood are seen as being quite transitory, taking up projects and then leaving them half-complete.

Type AB blood: If you have AB type blood, you get the best of both worlds. According to Ketsueki-gata, you’re likely to be regarded as rational, composed, sociable, and adaptable. But you can also be unreliable, critical, indecisive, and aloof. AB type blood is the rarest in Japan, so people with it are often seen as eccentric.

Type O blood: These individuals are confident, strong-willed, optimistic, and natural leaders. But they are also competitive, insecure, and likely workaholics. According to this system of thinking, Type O people are not meant to get on with type A people.

There are other blood types out there – Ketsueki-gata was only designed to account for these main types.

Ketsueki-gata’s darker origins

The knowledge that there are different blood types (initially ABO but later others) was quite novel at the time, having only been identified in 1901 by Karl Landsteiner, but there were plenty of contemporary scientific beliefs that sought to merge prejudicial thinking with biological determinism. And it seems blood, something all humans have, was a useful tool in this racialist toolkit.

Eugenics, the now debunked idea that human populations can be improved through selective breeding and population control, was all the rage in Western countries at the end of the 19^th century. To many eugenicist thinkers – and there were many outside of Nazi Germany – the blood types were an indicator of racial purity. For instance, type B blood was considered more degenerate, and was more abundant among “psychopaths, hysterics and alcoholics”.  

The influence of Western eugenic science also had significant impacts on Chinese and Japanese societies. For the latter, the emergence of eugenics coincided with a rise in nationalism and the push to modernize. As such, the science of blood types soon became entangled with Japanese ideas about race, as well as marriage and eugenics.

In 1916, a Japanese doctor called Kimata Hara published a paper connecting blood groups to personalities, especially national-cultural temperament. The idea was further linked to those salient among Western eugenicists by the German-trained Japanese geneticist and physician, Tanemoto Furuhata. 

Furuhata not only published influential research on serology in international journals, but also wrote in Japanese newspapers about blood-type character analysis at a time when the country was increasing its imperialist aggression. Then, in the late 1920s, a popular social psychologist called Tokeji Furukawa published a paper called A Study of Temperament and Blood-Groups which brought the idea to a broader audience.

Furukawa sensationalized and simplified the idea, merging research into the racial distribution of blood types with his own brand of psychological concepts. After this, the popularity of the idea ebbed and flowed until it took off again in the 1970s, when it was picked up by the journalist Masahiko Nomi.

From then on, Ketsueki-gata became a recurring theme within many books and self-help guides. It was especially popular for romantic and business guides that sought to help people navigate the uncertainties of life by explaining the compatibility between blood types. Movies and songs continue to reference it today and, despite its dubious scientific grounds – dubious here being a shorthand for “non-existent” – it has become popular in South Korea, Taiwan, and even the USA.

This article is part of Inconceivable series debunking unscientific stories on the Internet.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.