Flip-flops are popular summertime footwear with an onomatopoeic name derived from the sound they make when one walks wearing them. And beyond that sound, there is not a lot to them. Each pair is nothing more than a two pieces of shoe soles held in place on the appropriate foot by a typically y-shaped strap anchored between the first and second toe. Their simplicity is, probably, their greatest appeal.

And also the reason why the cause tens of millions of dollars in injuries each year — in the UK alone.

In 2010, the UK’s Daily Mail reported that England’s National Health Service (NHS) attributed roughly 200,000 doctors and emergency room visits to injuries “caused by wearing [flip-flops].” The total cost of those visits? 40 million pounds, or about $63.5 million. While that number includes all sorts of injuries not directly related to foot care, it speaks volumes to the size of the potential ills caused by the shoes.

In 2008, a doctoral student in biomechanics at Auburn University conducted a study using 39 college-age men and women. The participants in the study were asked to walk across a board — twice — which measured vertical force while a camera monitored their foot and leg movements. One of the two treks was made using flip-flops; the other was while wearing “traditional athletic shoes.” As reported by USA Today, the study found that “[w]hen participants [in the study] wore flip-flops, they took shorter strides and their heels hit the ground with less vertical force than when they wore their sneakers.” This change in the wearer’s gait can lead to foot and lower leg pain. Further, the study found that while wearing the flip-flops, participants “did not bring their toes up as much” as they typically would, perhaps because the toes were busy gripping the flip-flops. A review of the same study by CNN noted that this “seemed to result in problems from the foot up into the hips.” Flip-flop use has been linked to sprained ankles, pronation and misalignment of the foot and legs, flat feet, tendonitis, blisters, and more.

And those in the know practice what they preach. The executive director of the U.S.-based Institute for Preventative Foot Health, Bob Thompson, told CNN (in a separate story two years later) that flip-flops are so bad for your feet that he does not own a single pair.

Bonus fact : Flip-flops have a history dating back to ancient Egypt, but the ones commonly worn in the U.S. and Europe are probably originally from Japan. Per Wikipedia: “The modern flip-flop descends from the Japanese z?ri, which became popular after World War II when soldiers returning to the United States brought them back.” Zori were often considered formalwear for Japanese women of the time.

From the Archives: The Birth of a Shoe Company: How Kenneth Cole got its start (in a less-than-traditional way).

Related: A pair of zori.