If you're a Westerner familiar with K-pop, you've probably heard talk of different blood types. In Korea, Japan, and some other parts of East Asia, asking a person their blood type is as common as asking them their date of birth or their hometown. Many people believe that a person's blood type can determine their personality, and some people go as far as hesitating to date or hire a particular type that supposedly doesn't match well with their own blood.

As a K-pop fan, maybe you've seen it in this photo shoot actor Won Bin did where he posed as the four different blood types, in interviews where stars discuss their personality based on their blood type, or heard about HyunA's super knowledge about potential suitors and their blood types.  As strange as that may seem to some Westerners, it's not all that different than asking a new acquaintance about their astrological sign, although it's much more common in Korea to believe the theories about blood types than it is to put faith in astrology.

But where does that come from? We'll break everything you need to know about blood types right here.

Where did the idea of blood types determining personalities originate?

The idea seems to have been popularized in the 1970s by Japanese journalist Masahiko Nomi, who conducted years of research based off the blood type beliefs of Takeji Furukawa, a professor in Tokyo in the late 1920s.

Furukawa's initial research had a brief heyday. Later, though, it was discovered that he had conducted unreliable tests that had racist motives, and his theories were mostly tabled until Nomi picked them up in the 70s. In his 1971 book Understanding Affinity by Blood Type, Nomi published findings from interviews he says he conducted with more than 100,000 Japanese citizens who displayed different characteristics according to their different blood types.

The book became a sensation, and soon people wanted to know more about what blood types led to qualities like leadership and athleticism or which blood type pairs would make a good couple. One of the most cited statistics was about Type O's. They are supposed to be aggressive, realistic, and often highly energetic and focused - the qualities that many people look for in a leader. Nomi reported that since World War II, for instance, Japan's rate of Type O prime ministers was higher than the average rate of Type O's.

His original ideas have taken on new life in Korea and other parts of Asia, though. Some modern believers of blood type humanics (as Nomi labeled his studies) believe that once a person is born with a certain type, their temperament is sealed. Nomi had a little more faith in the flexibility of the human experience, however. He thought that blood type was simply one factor in a personality, with other factors including environment and nurture playing key roles.

Is there anything to it?

There isn't solid science backing up the blood type claims.

What scientists have found, though, is that there seems to be a self-fulfilling prophesy at work in blood type studies among those who strongly believe that their blood influences their personality. For instance, researchers have found that in self-reporting personality tests, people who believe they are a Type A, for example, will report in themselves characteristics that fall in line with the description of Type As. However, in studies where people did not know about or did not believe in the blood type claims, no major statistical evidence was found regarding personality and blood types.

That shows how alive and well the theories may be, and how those beliefs can factor in to people's perceptions about their own character or even choices in a partner or career path.

All in all, the science isn't really there, but that doesn't mean it's not kind of fun to speculate about what blood type you'd match with best, or which K-pop star has the most Type B energy. To paraphrase many scientists: it's not based in cold hard facts, but it is a fun conversation topic.

What do the different types of blood supposedly say about a person?

Type A people are supposedly the more introverted, artistic thinkers of the blood types. They have a calming energy, which makes them great listeners and very trustworthy, but also might be concealing their much more nervous, self-doubting, or sensitive inner thoughts. This can lead to perfectionism often found in Type As.

Type B's are known as the intuitive free spirits of the blood types. These are people that will accomplish any challenge presented to them, but once it is finished will choose the next adventure or obstacle to go conquer. They are most likely to find satisfaction and personal growth through meditation or other introspective activities.

Type O personalities are known as born leaders who exude power and confidence and are generally creative and productive people. On the downside, they thrive on that energy and can get angry, restless, or reckless when they are too stressed or fail at a challenge.

Type AB, like its name suggests, are an alleged mix of the types. It's often said that AB types have to work the hardest to maintain their best qualities, like being comforting, passionate, empathetic, wise, and loyal friends. If they don't take care of themselves, though, their worse side can come out, leading to a damaging lack of self-confidence.

Wondering what type of blood flows through your favorite star? Check it out here!