I Wore Flip-Flops in NYC for a Weekend, and This Is How Much Bacteria They Accumulated

New Yorkers can be quite opinionated about things, like owning a car while living in the city or wearing flip-flops on the streets. And when it comes to the latter, this editor is no exception.

I’ve always detested flip-flops, but I had always suspected they were disgusting, and I didn’t have any way of knowing for sure. As part of an FN experiment, I decided to take arguably America’s most popular summer shoe out for a stroll around NYC. That’s when I confirmed what I had already known: Flip-flops in the city are, yes, incredibly disgusting.

It began with a walk on the Columbia University campus. It hadn’t been more than an hour and a half before the inverted V-strap of the flip-flops started to form blisters on the top and sides of my feet. In the evening, I took them out to the grocery store — a 20-minute walk from my apartment. Despite the light sprinkling of rain, I spotted a few other flip-flop-wearing New Yorkers going about their business at the grocery store, Starbucks and the bank.

The following day, I braved rainy weather conditions to meet with my friend Zach, who was just as surprised as I was to see that the flip-flops had made it into my shoe rotation. We walked a 15-block stretch of Riverside Park to hit 91st Street Garden, followed by another 10 blocks to Cafe Lalo. (We’re both big “You’ve Got Mail” fans.)

The trip took us to the nearby Lululemon for a little retail therapy, but leaving the store empty-handed led us to famed hot dog chain Gray’s Papaya and a sports bar on the Upper West Side. At this point, the rain had crescendoed into a full-blown storm, but Zach and I stayed put with our brewskis and the MLS game on multiple screens. I’d be lying if I didn’t say I was wary the whole time about locals accidentally spilling their drinks on my bare feet.

An hour or so had passed, and the torrent settled. We continued our journey, braving the wet conditions in Central Park, where we passed by numerous kinds of flora and fauna, as well as tall grass, gravel, soft soil and rain-soaked road — all home to terrifying creatures and organisms I was sure latched onto my skin. The damp environment was a challenge to navigate, as I kept slipping and sliding but luckily avoided any major mishaps (that’s why picking out a pair of flip-flops with arch support and cushioning is so key).

When I arrived home that night, the blisters had solidified into three red, sore bumps. I crafted a homemade scrub and exfoliated every surface below my knees for a solid hour. A day later, I sent the flip-flops over to North Carolina-based antimicrobial company Microban, which provides odor control technology to footwear brands around the world, to test just how much bacteria had accumulated on my shoes after a weekend of wearing them on NYC streets — with their collections of litter, human and animal waste, germs and other infectious agents.

Flip-flops sent for Microban bacteria testing
My Havaianas flip-flops, ready for testing.
CREDIT: Microban

The result? Hundreds of thousands of colony-forming units of bacteria (or CFUs) on a single flip-flop alone.

The process went as follows: First, a sterile swab was wet with saline, and a one-square-inch area was swabbed in three directions to remove any organisms present on the left shoe sample.

Flip-flops sent for Microban bacteria testing

It was then placed in a tube with 10 milliliters of sterile saline and “vortexed” for one minute to distribute swabbed organisms throughout the saline.

Flip-flops sent for Microban bacteria testing

A 1-milliliter sample was pipetted from the saline tube and plated on tryptic soy agar, a ubiquitous, nonselective nutrient source for microorganisms, and further dilutions were made.

Flip-flops sent for Microban bacteria testing

Finally, the plates were incubated at 36 degrees Celsius (or 96.8 degrees Fahrenheit) for 48 hours to ensure the growth of all present microorganisms.

Breaking down the numbers, the toe area of the top of the flip-flop collected the most amount of CFUs at 260,000, with the middle at 110,000 and the heel at 300.

Flip-flops sent for Microban bacteria testing
Bacteria from the top of the flip-flop.
CREDIT: Microban

For the bottom of the flip-flop, the toe area gathered 1,000 CFUs, the middle an equal amount and the heel 230.

Flip-flops sent for Microban bacteria testing
Bacteria from the bottom of the flip-flop.
CREDIT: Microban

It certainly didn’t help that the weather during the weekend of wear was humid and rainy, allowing bacteria to thrive. This explains why the top of the flip-flop contained a much higher number of CFUs than the bottom.

“Bacteria need certain things to grow and survive — food source, moisture and a place to grow that meets their environmental preferences,” reported Katherine Harrell Hawley, senior microbiologist at Microban, who conducted the test. “The top of the flip-flop is in contact with the bottom of the foot, which provides all of the above — dead skin cells for a food source and a warm, moist environment from the contact with the bottom of the foot.”

Gross? Yes. Likely never to wear them again? Absolutely. If the above imagery and scientific testimony didn’t dissuade you from ever wearing flip-flops in the city, wait until you’ve seen a flattened rat on the sidewalk or been splashed by unidentified liquid in the middle of the street.

One thing’s for sure: This editor has completely sworn off flip-flops. (Except, just maybe, at the beach.)

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