"The Japanese have found a new way to ‘typecast’ people. It’s not astrology; it’s not studying the bumps on people’s heads. It’s blood typing. There is absolutely no scientific basis for typecasting by blood, of course, but that hasn’t stopped many Japanese from applying it to everything from love affairs to employment interviews."

-Newsweek 1985

Left: Japanese women’s magazines help ladies determine their Prince Charming’s perfect blood type. [Credit: Pen.Rev]

People throughout history have sought to categorize themselves and each other. For example, Hippocrates (406-377?B.C.) and Aristotle (384-322B.C.) attempted to classify personalities according to bodily humors and blood. According to social scientists, this recurring desire stems from an urge to define the self and others in specific social and cultural roles. In 1930, Tokeji Furukawa contributed to the classification efforts by choosing blood as a physiological classification characteristic; Furukawa’s assertions caused an impact that would shape the next eighty years of popular Japanese culture.

Furukawa’s research claimed that individual blood types—A, B, O, and AB—reflected the personalities of those who carried them. Using questionnaires but providing no controls or statistical tests, Furukawa presented intricate behavioral charts defining the various blood types and concluded that a correlation between blood types and personality exists. As the study lacked empirical evidence, in 1936 G. N. Thomson refuted Furukawa’s arguments but was followed by a wave of pro- and anti-counter arguments throughout the 1960s and 1970s. In the 1970s numerous books revived public interest in the subject, peaking in 1984-1985 with a total of 204 publications discussing the link between blood type and personality. From this foundation, blood type categorization, or ketsueki-gata, firmly established itself into Japanese culture.

Ketsueki-gata permeates numerous levels of Japanese society, from romance to work. Appearing in a 1990 issue of Asahi Daily, a Japanese national newspaper, Mitsubishi Electronics announced that a team composed entirely of AB type workers had been selected because of "their ability to make plans." Similarly, kindergarten classrooms are sometimes divided into blood types so that individual teaching techniques can be tailored to blood group personalities. In romance, things become even more complex; young Japanese commonly exchange blood types upon first meeting, thus providing a supposed valuable source of insight into the other person. Popular Japanese women’s magazines combine blood types with the western zodiac signs, additionally synched to four elements (air, earth, water, fire), producing "Love Biorhythm Graphs." Meshing 16 different female types with 16 different male types, a chart providing 256 fortunes for "You and your boyfriend’s love compatibility" allows a woman to assess a mate’s inherent compatibility and strategize accordingly.

In addition to revealing personality, explanations for ordinary illnesses can be divined through blood types. Popular publications from drug stores and health magazines discuss self-diagnosis through a reader’s blood type, including propensities towards certain types of medical maladies associated with blood types. Using blood types as a means of diagnosis and treatment harkens back to the original Chinese medical influence in Japan that lacked an emphasis on actual disease. The Chinese historically blamed diseases on an imbalance of bodily energies and substances, thus perpetuating the concept of ketsueki-gata by grounding it in a historic cultural context.

Left: Blood type bath salts, one of the many customized blood type products available in Japan. [Credit: flickr – kenleewrites]

Surveys show that the majority of Japanese citizens believe in ketsueki-gata to some extent. A 1986 survey by M. Toyama found that 96 percent of 105 Aoyama-Gakuin University students thought blood types influenced personality, while only four percent declared no relationship between the two; random surveys (pdf) in 2002 of 1102 Japanese found 75 percent believed in ketsueki-gata. However, no scientific evidence exists to support it. In the journal Personality and Individual Differences, Mary Rogers and Ian Glendon discussed the flaws of "scanty" and "conflicting" studies supporting the blood type theory. Egregious scientific errors, such as including no quantitative data, violating statistical rules, having flawed methodologies, presenting inconsistent results, not testing for confounding variables, and performing no multivariate statistical analyses, all contribute to the evidence that no connection exists between a person’s blood type and personality. For example, a 2000 pro-blood typing publication by Peter D’Adamo and Catherine Whitney presented no quantitative data to support their claim and used a self-selected sample of respondents.

To put blood typing to rest once and for all, studies were conducted to determine an association between personality and blood type. In the same 2003 Rogers and Glendon study, the authors tested 60 Australians for associations between their blood types, gender, and personality factors through two different well-established personality tests. In 2005 Kunher Wu and colleagues surveyed 2681 Taiwanese high school students (blood typing is also popular in Taiwan), using the widely accepted five-factor personality model for assessment and controlling for confounding factors such as preexisting blood type belief, academic achievement, and body mass index. Neither study found a significant relationship between personality and blood type, rending the theory "obsolete" and concluding that no basis exists to assume that personality is anything more than randomly associated with blood type. Rogers and Glendon also asked researchers formerly supporting the theory to "more fruitfully" turn their attention elsewhere.

Although researchers have established that no scientific basis exists for ketsueki-gata, why does the theory continue to pervade popular Japanese culture? According to Tokyo Woman’s Christian University psychology professor Kiyoshi Ando, blood types could be a convenient topic of conversation, hold appeal as a predictor of destiny and behavior, and can serve as an outside authority for people to rely upon in order to avoid complex thinking and judgment. At extremes, blood typing can influence how people understand and describe their world, how they define themselves, and shape how decisions are made.

Ketsueki-gata may manifest itself as prejudice and discrimination, Ando pointed out, providing a very real hazard to society. For example, a survey found that a "negative impression" of those with AB blood type—composing a 10 percent minority group in Japan—exists amongst Japanese high school students. At its worst, blood typing causes negative influences on interpersonal and professional relationships, providing an unsound means by which persons are judged and compared with others.

Right: Don’t forget your customized blood type towels to dry off from your blood type bath. [Credit: flickr - MShades]

And blood typing is not confined only to Japan. Donna Gates, nutritional consultant and author of The Body Ecology, credits her "special relationship" with Japan for introducing her to the merit of ketsueki-gata. Using her knowledge of blood types to shape her work with autistic children and design specially tailored diets for persons of each blood type, Gates writes on her website that, "While there is not a lot of ‘hard science’ to date on blood types, it makes a lot of ‘common sense’ to look further into this theory." She urges readers to forward the article to friends and family as a "fun experiment" comparing their blood types and discovering how valid her arguments may be. Gates’ book has sold more than 180,000 copies. Other Western authors have cashed in on the trend, publishing books ranging from blood type diet to allergies.

The truth is, however, that not much information exists for developing an informed opinion about the validity of blood typing. In a Google search of "blood type personality," the first pages to appear are those detailing the "science" of blood type personality, and they can be quite convincing. At one site, for example, readers can find labeled chemical structures of blood types and detailed analyses to clarify further the "science." True science is doing a poor job of conveying its counter-message, so pseudo-science dominates. Until scientific communicators step up, blood types can continue to influence everything from condom usage to dairy intake in Japan and beyond.

About the author: Rachel Nuwer is a graduate student at New York University’s Science, Health, and Environmental Reporting Program. Her keen interest in science and nature was fostered in the bayous of southern Mississippi. Taking this love to an extreme, she investigated illegal wildlife trade in the peat swamp forests of Vietnam for her ecology master’s thesis at the University of East Anglia, England. When not writing about science Rachel can be found taking photos, exploring the world, or rehabilitating stray kittens.

The views expressed are those of the author and are not necessarily those of Scientific American.