12 Things You Need to Know Before You Wear Flip-Flops

Ancient Egyptians wore thong sandals as many as 4,000 years ago, according to the Sheridan Libraries at John Hopkins University. The average slides used coiled papyrus or palm leaves, but King Tutankhamun owned an especially-elaborate pair with gold and bone inlay.

Americans started buying Japanese-made sandals, called "zori," in the 1950s. The hyphenated name arrived a decade later, according to the New York Times. Beach-goers dubbed the thongs "flip-flops" after the slapping sound each heel makes.

Strapless sandals make your toes grip extra-hard and alter the normal heel-toe motion, says board-certified podiatrist Dr. Grace Torres-Hodges. "You have to physically keep it on your foot," she explains. "If the foot's already working that way, it can't focus on walking." That extra work can lead to painful problems like hammer toe, tightness in the achilles tendon and plantar fasciitis. 

Thanks to the shoes' open nature, flip-flop wearers take smaller steps than their sneaker-clad friends, according to a 2010 study by Auburn University.

Flip-flops change how you stand mechanically. "Because you don't have the right support, that can translate to movement or correction in the knees, hips and back," Torres-Hodges says.

In 2007, Tropical Smoothie Cafe dubbed the third Friday of June "National Flip-Flop Day" to celebrate the chain's 10th anniversary. That makes June 16 this year's day of honor. 

Tropical Smoothie Cafe will give flip-flop-wearing customers a free Sunshine Smoothie in a limited-edition cup — but only on National Flip-Flop Day, of course.

The Northwestern University women's lacrosse team sparked a national "kerfuffle" when several players wore flip-flops to meet President Bush. After fashion experts called the shoes inappropriate, the athletes auctioned them off to benefit a young fan with cancer.

President Obama became the first president photographed in flip-flops while vacationing in Hawaii. His toes set off a media firestorm — and even made the cover of the New York Post.

A collaboration between L.A. artist David Palmer and footwear company Chipkos, the since-discontinued shoes lacked gems or jewels. The big bucks actually went towards preserving 100,000 square feet of Costa Rican rainforest, Time reports.

Besides messing with your stride and posture, the shoes can inflame the joint by your big toe. "If it keeps hitting up against the ground it will become inflamed and swollen," Torres-Hodges says.

Good news: You can keep your favorite shoes after all, as long as you wear them in moderation. For extra comfort, Torres-Hodges recommends pairs with fitted beds and support for the arch and ball of your foot. Then save those sandals for the right occasion — like a well-deserved day at the beach.