While stationed in Japan or Okinawa, you may have had what seemed like an odd question presented to you by a stranger at some point.

“What is your blood type?”

While your blood type is extremely important to know for medical purposes, why would someone you just met ask you a question like this?

In Japan, many believe you blood type tells of your personality and relationship compatibility.

I can’t deny that I often find myself stereotyping people based on their blood types. I’ll find myself unconsciously judging a person that I know little about other than their blood.

And I’m not alone. According to a 2010 study by ISHARE, 74.8 percent of 567 males and females (ages 20-49) said they believe in the blood type theory of personality. In fact, blood type is an indispensable way to profile politicians and celebrities in Japan these days. TV programs and magazines often run coverage of blood types and personalities. Yoko Funasaka, a housewife who runs a liquor shop with her husband in the center of Tokyo, says she often find herself stereotyping based on blood type without realizing it.

“If the person seems too nervous, I assume his blood type is A before asking him for it,” Funasaka says.

“I get discouraged when I have to work with an AB person,” added her son Masahiro. “Type AB people change their thought very frequently, which often irritates me.”

One of the most accepted theories is that a blood type-A person is a serious and sensitive perfectionist that is also anxious and stereotyped. Type B is cheerful, liberal, eccentric and suspicious, while O is emotional, generous, stubborn and selfish. An AB person is rational and sociable but mysterious and unpredictable.

The theory also suggests blood types A-O, A-AB, O-B, B-AB pair well, while A-B, O-AB are opposite characters and have a relatively hard time getting along. Matching blood types (A-A, B-B, etc.) also don’t pair well.

So, who invented this unique theory?

Originally, ABO blood types were discovered by Austrian scientist Karl Landsteiner in 1901, and this Nobel prize-winning work made it possible to identify the different blood groups and enabled blood transfusions to be carried out safely.

Masahiko Nomi, a Japanese journalist who had no medical background, researched the relationship between the four blood types Landsteiner discovered. He tracked the difference of personalities, and published several books on the topic, such as “Anthropology by Blood Type” and “Essence of Blood Types,” in the 1970s.

With the huge success of these books, Nomi’s blood-type theory of personality was rapidly accepted throughout the nation.

Today, many Japanese consider his theory a strong strategic tool in learning the personality of others and building effective human relations. The theory is basically considered common sense among Japanese.

In fact, some companies and sports teams try to build teams or groups in accordance with the theory. They customize training for players or employees, and some directors and managers make decisions on personal assignments or recruiting based on the theory, as well.

Although the theory provides a fun topic in daily conversation, it has also led to prejudice, harassment and discrimination.

In fact, asking blood types during job interviews has repeatedly been a social issue in Japan, and the government has been suggesting employers not include questions regarding blood types in recruiting process, as it may result in discrimination.

Yukihiro Ooyama, a Tokyo salaryman, experienced the prejudice during his school days.

“Because of my blood type O, my friends kept telling that I was a coarse and spineless, and that weighed on me,” Ooyama said. “Their repeated association finally drove me feel I should have the personality that the theory suggested.”

Keisuke Yukaji, a delivery agent in Tokyo, says that people would always change their ways of looking at him when they heard his blood type was B.

“Because a B person is considered as careless and eccentric, I think people think less of me when they find out my blood type.”

Most scientists, however, are skeptical about the theory and try to debunk it. Dr. Kengo Nawada of Kyushu University said that there is no evidence to support the theory after researching 10,000 people in 2014. Even with no scientific evidence, the theory remains very popular. It is deeply rooted among the Japanese and will likely control our perspective for generations to come.

“It doesn’t matter if it is a scientific fact or not, but I think it sure works,” Funasaka said. “Japan is a kind of homogenous society, and the theory provides a simple framework to divide us into easily recognizable groups.”

Now, if you’re ever asked about your blood type by a local, you know why. And if you’re type B and meet someone local that rejects you, there’s a good chance that person was an A-type, and they realize that you might not be their best match.

But don’t worry. I am an A-type male married to a B-type wife, and we have been together for the last 25 years. So, does our relationship disprove the theory, or are we just the exception to the rule?

takiguchi.takahiro@stripes.com

Blood types & characteristics

ASerious, meticulous, careful and sensitive perfectionists, but sometimes too anxious, pessimistic and stereotyped. They try to restrain desires and emotions and obey orders, rules and customs. They avoid extremity and don’t make a racket.

OEmotional, vital and generous, but sometimes too stubborn, bossy and selfish. While they love friends and family, they are extremely wary of strangers.

BCheerful, innovative, flexible and liberal, but sometimes too careless, eccentric and suspicious. They never lose their own pace in life. They don’t care about criticism by others.

ABRational, kind and sociable, but sometimes too mysterious and unpredictable. They have coexistence of two different characters, stabled emotion and capricious feelings. They don’t want to become too intimate to a person.

Personal matching & blood types

Best Matching: A-O, A-AB, O-B, B-ABRelatively hard to match: A-B, O-AB (opposite characters),A-A, B-B, O-O, AB-AB (same characters)

Source: Essence of Blood Types by Masahiko Nomi

Famous Blood

Donald Trump, David Cameron, Steven Hawking, Steve Jobs, O.J. Simpson

Elvis Presley, Queen Elizabeth, Al Capone

Bill Clinton, Albert Einstein, Bill Gates, Michael Jackson, Paul McCartney, Jack Nicholson

Barack Obama, Hillary Clinton, Vladimir Putin, Walt Disney, John F. Kennedy, Marilyn Monroe

Source: whatsmyblodtype.org & answers.com