Sam Hobert, 19, has suffered for his flip-flops. A few years ago, he broke his right big toe after slamming his foot into a rock while hiking in New Hampshire in his favorite summertime footwear. On a warm day a few weeks ago, the George Washington University freshman was nursing foot blisters, courtesy of a pair of new brown leather ’flops from the Gap.

“It’s looks over comfort,” he says. “But I’m regretting it a little bit, I’m not gonna lie.”

It’s springtime and flip-flops — the airy sandal with the distinctive thwack-thwack soundtrack — are back, much to the frustration of podiatrists (but to the delight of their billing departments). Wearing flip-flops can cause problems ranging from stubbed toes and cuts to overuse injuries such as foot stress fractures.

Now that the weather is warm, says Howard Osterman, a podiatrist who has practiced in Washington for 20 years, he will see at least one patient with a flip-flop injury every day through September.

Osterman treats a lot of tourists whose flip-flops aren’t up to rigors of eight-hour days tromping across the Mall — “kids from Wisconsin who didn’t know they’d need a podiatrist when they went on vacation,” he said.

Sandal (BigStockPhoto)

But the “main culprits” doing themselves damage, he says, are young staffers and interns on Capitol Hill who pound the marble floors of Congress in flip-flops (hopefully on their way to change into more professional footwear) or ballet flats.

The No. 1 problem he sees from the shoes are overuse injuries such as stress fractures of the metatarsals, the five long bones that reach out to the toes. A stress fracture happens after constant, repetitive stress to a bone and is generally treated with rest, more-supportive shoes and perhaps a walking boot.

Many of the less-expensive flip-flop styles consist of just a flat piece of rubber and the toe thong. The lack of arch support can cause another common foot injury: plantar fasciitis, inflammation of the thick band of tissue along the bottom of the foot that causes a stabbing pain, especially in the heel. People with flatter arches are more prone to such overuse injuries because they need more support for their muscles and ligaments, Osterman says.

Flip-flops also leave the feet unprotected and exposed to the elements, which can mean cold toes, sunburns, cuts and bruises.

Very few studies have looked at the pros and cons of flip-flops. In 2008, Justin Shroyer, a biomechanics graduate student at Auburn University in Alabama, studied 39 college-age men and women to see how they walked when wearing flip-flops compared with sneakers. A native Floridian and a lifelong fan of flip-flops, Shroyer was inspired to study the shoes when he noticed how many fellow students wore them all day long and when he realized that it was a practically untouched area of research in biomechanics.

Shroyer, now an assistant professor at the University of Louisiana at Lafayette, found that while wearing flip-flops, participants in his study took shorter steps. He hypothesized that this was because the wearer was trying to get his or her foot on the ground faster, to prevent the shoe from flying off. Also, flip-flop wearers did not bring their toes up as much during the leg’s swing phase because they tended to grip the sandals with their toes.

“Your toe flexors are fighting what you’re naturally trying to do,” Shroyer says. “It’s kind of an antagonistic push-pull, tug-of-war going on, and it’s not happening in running shoes or bare feet.”

The researchers speculated that the altered gait could result in pain from the foot up into the hips and lower back.

A 2010 study by Rush University Medical Center in Chicago found that flip-flops and sneakers with flexible soles were easier on knees than clogs or special stability shoes. The researchers analyzed the gaits of 31 people with osteoarthritis of the knee while they wore the various types of footwear.

Thonglike sandals have been around at least since the ancient Egyptians, according to Elizabeth Semmelhack, senior curator at the Bata Shoe Museum in Toronto, founded by the family behind Bata shoes. Flip-flops as we now know them were inspired by the traditional Japanese zori sandal, worn with kimonos, and originally marketed to American women after World War II. The style became popular in the 1950s and ’60s with the rise of surfer culture and then walked its way into mainstream fashion in the 1990s, Semmelhack says.

Flip-flops have come a long way from the $5.99 bin at the gas station.

Nicole Camier, 27, was wearing black, rhinestone-studded flip-flops one sunny late-March day in downtown Washington. She was hustling to a job interview, where she planned to change into a pair of heels.

Camier owns about five or six pairs of flip-flops and wears them because they’re “comfortable and easy,” she said. “When it’s raining, I find myself slipping and sliding, but normally I don’t have any problems.”

Moira Lewis, 23, sported a pair of paisley-print Kate Spades last month. She wears one of her three pairs of flip-flops every day in the summer, she says. This year, she started wearing them in early March.

“It was probably a mistake,” she says. “It was too cold.”

Osterman doesn’t suggest avoiding flip-flops entirely, but he says that people should wear them in moderation — for a few hours on the beach or at the movies, for example.

Shoppers should look for flip-flops with a stable sole, he says. Brands such as Reef, Rainbow, FitFlops, Teva and Merrell make models that throw more of the weight into the heel and out of the forefoot, he says.

“When you only have something between your toes to keep the shoe on, you have to curl your toes excessively,” Osterman says. “You have to spend all day firing your muscles to keep the shoe on the foot.”