Spend any length of time in Japan and you will at some point inevitably be asked what your blood type is. One may be taken aback by this at first. Was there an accident? Do they need a blood transfusion and this is a desperate plea for help? These things may flash through your mind in response to such a bizarre and off-kilter question. However, rest assured it is actually nothing of the sort. Indeed, in Japan this is akin to asking someone what their star sign is, but with the added weight that many people really truly believe it. Welcome to Japan, where your blood truly makes you what you are.

There is a long history of belief in the idea that the blood influences our character and even our destiny, and this was being investigated well back into history. Aristotle spoke of this possible connection, and the great Hippocrates also sought to establish a solid link between the quality of one’s blood and personality. This all got a boost of sorts in 1901, when the Austrian scientist Karl Landsteiner established the ABO system of blood grouping, which places human blood into four basic types: A, B, O, and AB, and which also won him a Nobel Prize. Although this groundbreaking research would pave the way for safer blood transfusions and save countless lives, it also unfortunately opened the door for these concrete blood types to be twisted and used by eugenics theorists as a basis to judge people based on blood type alone, giving the ancient belief in a connection with blood and personality a basis in reality for them.

This was most famously carried by the Nazis, who sought to use blood types as a basis to establish a stronger claim of racial superiority and purity, but it also found its way to Japan in the 1920s, when the country was quite militaristic and looking for ways to find the perfect soldiers for different duties or roles. In 1926 an article was published in the Army Medical Journal entitled Blood Type Biological Related by Rin Hirano and Tomita Yashima, establishing the pseudoscientific idea that blood types were a reliable indicator of one’s personalty and aptitude in different areas. This work would be followed up on by a professor named Takeji Furukawa the following year, in an article titled The Study of Temperament Through Blood Type, in the scientific journal Psychological Research.

This was all presented as serious scientific research, and the Japanese government and populace ate it all up. Before long there were whole military units divided by blood type, and officers were invariably promoted or assigned based on this. They also used it to racist ends, using blood type as a basis for widespread discrimination against the Taiwanese and the indigenous Ainu people of Hokkaido, funding numerous studies in an effort to prove they were mostly of one blood type or the other. This all slowly went out of fashion in later years, but was brought back in a big way in the 1970s, when new books on blood types started becoming popular, in particular those by a journalist and author named Masahiko Nomi, who between him and his son published dozens of books on the matter, and the whole practice became en vogue again. Many other books on the subject have followed, and they are frequently best sellers in Japan.

The practice of asking for people’s blood type and of basing a horoscope of sorts around it took off, particularly among young women, who believed it was integral to finding a compatible mate. Countless magazines, books, and TV shows in Japan have continued to talk about the influence of blood type on abilities and personality right up into the present, and the extent of how much a person’s blood type has influenced decisions in Japanese culture even in modern times is a bit startling. Some baseball or other sports teams have based recruitment based on blood type, and companies routinely ask potential job prospects to write their blood type down on resumes. It is known that some kindergartens even divide classes into blood types, and some companies structure entire divisions, duties, and leadership positions based on blood type. There are even whole product lines for things such as shampoo, chewing gum, and soft drinks marketed and catering to certain blood types, and there are whole diet programs devoted to what works best for people of one blood type or another. It is all rather bizarre to say the least.

There have even been public scandals revolving around blood type, such as in 2011, when Minister for Reconstruction Ryu Matsumoto resigned after making insensitive statements to local officials in the wake of the big Fukushima earthquake and publicly blamed his blood type B for it. The dark side of all of this is the potential for discrimination based on all of this, of which there is unfortunately plenty. People have been turned down for jobs based on their blood type, or assigned into roles they were not suited for simply because their blood type deemed them appropriate for the job. The idea of blood types holding sway over one’s characteristics is also huge in the dating scene, where your blood type can easily determine whether a woman or man decides to go out with you or not. Bullying based on blood type is also common, and there is even a word for this in Japanese, bura-hara, or “blood harassment.” Considering that it is estimated that 80% of Japanese people between ages of 20 and 49 truly believe in this blood type personality theory, this is kind of a big deal.

So, is there anything to this all? Well, this largely depends on who you ask. The mainstream scientific opinion is that there is no empirical data whatsoever that shows any noticeable link between a person’s blood type and their personality traits or affinities. However, there are still those studies that seek to prove a relationship between the two, and these have been carried out all the way up to the present, to mixed results, and they are mostly seen as fringe efforts that do not follow strict scientific protocols. As of yet, there has been no conclusive evidence that there is any correlation whatsoever, but that has not stopped the belief that this exists one bit.

By now you are no doubt wondering just what exactly your blood type is said to mean for you. Well, assuming you even know what your blood type is, as most Japanese do, let’s start with Type A. People with this blood type are said to be sympathetic, sensitive, calm, patient, careful and cautious to a fault, nit-picky, responsible, kind, obsessed with cleanliness, hard workers, perfectionists, hard to please, high strung, worriers, and unable to relax. Famous Type A blood types include Britney Spears, Ringo Starr, and, gasp, Adolf Hitler.

Type Bs are optimistic, fun-loving, adaptable, happy-go-lucky, carefree, attention seekers, flexible thinkers, resourceful, creative, pragmatic, individualistic, wild, and unpredictable. Famous Bs are Leonardo Di Caprio and Jack Nicholson. Type Os are supposed to be realistic, curious, ambitious, cautious, loyal and devoted, leaders, romantic, strong and often bullheaded, passionate, stubborn, vain, and jealous. Famous Os include Queen Elizabeth II, John Lennon, Elvis Presley, and Paul Newman. AB people are said to be cool, controlled, complicated, mysterious, have an interest in various things, unique, artistic, unpredictable, spiritualistic, sensitive, rational, sociable, but also a bit stand offish. Famous AB Types include Marilyn Monroe and Mick Jagger.

So which one are you? Is it accurate? There is probably no basis to any of this in fact, but it is very intriguing that the Japanese should believe this so wholeheartedly. It almost goes beyond even zodiac signs in the United States, and people will really immediately form an opinion from a sort of idea about you based on how you respond to their question about your blood type. It is surreal. Although there is no known evidence of there being anything to this all, the habit of believing that blood type affects personality is ubiquitous in Japan, and its history as colorful as it is dark. So if you are ever in Japan and someone asks your blood type, well, you now know what they are talking about.