On a 95°F day, when you’re drenched with sweat and desperate to cool down, a swimming pool might look like the most beautiful thing you’ve ever seen. But to the people who study pool water for a living, it’s more like a warm, lightly chlorinated broth of everything a few dozen bodies carried in with them. That’s not a reason to stay on dry land—but it isa reason to know the handful of habits that can tip a day at the pool from refreshing to regrettable
We asked infectious disease doctors and water-quality experts which hygiene mistakes they see most. Here’s what you’re probably getting wrong—and what to do instead
You think chlorine zaps everything the second it hits the water
Chlorine is a genuinely great disinfectant, but it doesn’t work instantly, and it’s not all-powerful
Ordinary bacteria don’t stand a chance: “Chlorine, when it comes into direct contact with bacteria, in less than a minute, that bacteria dies,” says Kelly Reynolds, an environmental microbiologist at the University of Arizona who studies how pathogens spread. But a virus like hepatitis, which can be contracted through water, can take about 15 minutes. And the Cryptosporidiumbug—the single most common cause of pool outbreaks in the U.S.—can live in chlorinated water for roughly 10 days. To kill it, operators have to “shock” a pool with around 20 times the usual chlorine, and even that takes hours. Most of the time, though, Crypto is removed gradually as the pool’s filtration system continuously circulates and filters the water.
In other words, a swimming pool isn’t one giant bottle of Purell. Reynolds has watched people wipe a kid’s nose or change a diaper and then rinse their hands in the pool, figuring the chlorine will handle it. “They think of pool water as a sanitizing liquid, and it’s not,” she says—a pool runs around one part chlorine per million parts water, while hand sanitizer is about 60% alcohol
That’s also why you don’t want to swallow any of it: You wouldn’t gulp bathwater after a few other people had been soaking in it, Reynolds says
You skip the pre-swim rinse
Almost nobody showers before getting into the pool, which is a shame, because it’s one of the easiest ways to make the water cleaner for everyone. A quick rinse knocks off sweat, sunscreen, body oils, and—let’s be honest—the traces you carry from the bathroom, so you’re not dumping that load into the shared water or feeding the germs already in it
“If you shower before, you could help keep the pool cleaner,” says Lisa Cuchara, a professor of biomedical sciences at Quinnipiac University who teaches a course called “The Infections of Leisure,” about the germs people encounter while swimming, traveling, camping, spending the day at the spa, and pursuing other recreational activities.
But, “if you shower after, you could help prevent yourself from coming down with something,” she adds. A second shower washes away whatever was floating in the water, as well as the chlorine that can dry out your skin and hair.
Neither one has to be elaborate. If your pool has one of those little rinse-off showers by the deck, 30 seconds before you get in—and another quick rinse when you get out—goes a long way
You get in with an open cut, scrape, or fresh surgical site
Your skin is a remarkably good barrier—right up until there’s a break in it. Chlorine doesn’t magically seal a shaving nick, scraped knee, or healing surgical incision
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“When people have open wounds and then they go into the pool, they’re exposing their body to a lot of potential pathogens,” says Dr. Daniel Egan, an infectious disease specialist at Orlando Health. “It’s true that chlorine reduces risk of infection in these pools, but it never sets it to zero.”
How much that matters depends on the wound. A small cut isn’t much of an issue, Egan says; a large abrasion or a surgical site is—and the risk climbs in untreated water like a lake or the ocean. “Ideally you don’t want to jump into a pool when you have an open wound,” he says. “But if you do, change the dressing. Make sure it’s dry.”
That means sealing it with a waterproof dressing (such as Tegaderm), rather than a standard bandage, before you get in. Once you’re out of the pool, pat the skin dry and replace it with a fresh dressing. And if you’ve recently had surgery, don’t assume you’re ready to swim just because the stitches are out. Your skin may still be healing, so get clearance from your doctor before jumping in
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You never wash your feet
“Don’t get me started on feet,” says Dr. Alok Vij, director of dermatologic surgery at Vitalogy Skincare in Austin. Then he gets started on feet: They’re “one of the body’s highest-bacteria zones,” he says, along with the face, underarms, groin, and hands. Which makes it all the more alarming that “most people don’t wash their feet, period,” he says
Research suggests the more often people lather up their feet with soap, the fewer bacteria they tend to carry there. Going from washing once a day to twice a day drops the bacterial load on your skin dramatically. One of those bacteria is Pseudomonas, which also thrives in under-sanitized pools and happens to cause swimmer’s ear. In other words, that classic summer ear infection may have started on someone’s foot
So give your feet actual attention in the shower—especially before you swim—instead of assuming the water running over them counts as washing. This is especially important if you’re coming from the beach: Sand clogs a pool’s filters, and a pool that can’t filter can’t clean itself
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You pee in the pool
Most people file this one under gross-but-harmless. Yet peeing in the pool is actually “really bad,” Cuchara says
The reason is chemistry, not germs. Urine reacts with the chlorine that’s supposed to be killing germs and uses it up, producing chloramine: that unmistakable “pool smell” many people mistake for cleanliness. Every bathroom break you skip makes the disinfectant weaker for everyone else
That’s why the ocean gets a pass. “The urine itself isn’t the problem,” Cuchara says. There’s no chlorine out there to sabotage, and the volume is, well, the ocean. “The whales are peeing in the ocean,” she points out
In a pool, there’s no way around it: Get out and use the bathroom.
You marinate in a wet bathing suit
The instinct to lounge around in a damp suit all afternoon is working against your skin. Waterlogged skin is more permeable, and a wet suit keeps it that way. “It’s like a party of fungus, yeast, bacteria, and viral agents,” says Dr. Kimberly Eickhorst of Dermatology Associates of Western CT—all of which love a warm, damp, dark environment and are happy to set up camp when your skin barrier is softened
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She commonly sees “hot tub folliculitis,” an itchy, pimply rash caused by Pseudomonas bacteria that thrives in hot tubs. Patients arrive baffled, and her first question—”Have you been in a hot tub?”—often cracks the case
Change out of your wet swimsuit as soon as you’re done swimming, then take a quick shower. You’ll wash away chlorine, help restore your skin’s natural pH, and make it a lot harder for unwanted microbes to settle in
You assume your swimsuit cleans itself
Just because it spent all day in the water doesn’t mean it’s clean. Your suit is still carrying your skin cells, body oils, sunscreen, and whatever else was floating around in the pool
“You wash your underwear every time you wear it,” Vij points out, and you should treat your swimsuit the same way
Left unwashed, a swimsuit becomes a breeding ground for fungus and bacteria. At minimum, rinse it thoroughly in clean water before letting it dry, which also helps flush out chlorine and sunscreen that can damage the fabric; using detergent does an even more thorough job
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You let your ears drip dry
“A pocket of still water sitting in the ear canal is a recipe for disaster,” Egan says. There are always microbes living on your skin, and trapped moisture gives them exactly the environment they need to multiply.
That’s why swimmer’s ear isn’t just about swimming. It’s also about what you do when you get out. The infection occurs in the outer ear canal; it’s not the deeper kind that usually follows a cold
After swimming, tilt your head side to side to let trapped water drain, then gently pat the outer ear dry with a towel. The goal isn’t to get every last drop—it’s just to avoid leaving water sitting there for hours
You keep reaching for the same damp towel
Towels seem harmless, but they’re what dermatologists call a fomite: an object that can carry germs from one person to another
The germ Eickhorst worries about most is molluscum contagiosum, a common childhood skin virus. It’s benign, and it runs its course. It’s also unsightly and itchy. “We’re always counseling our patients: don’t take baths with siblings, and don’t share towels, because the virus can be transferred,” she says
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The other half of the problem is the towel that’s been sitting in the bottom of your swim bag since yesterday. “If you looked at it under a microscope, you would see some things,” Cuchara says. Though the real-world risk is low, she still recommends bringing a fresh towel every pool day
You let little kids turn the pool into a bath
Ask Reynolds what makes her cringe, and she points straight to the shallow kiddie pool. “We put the population with the poorest hygiene and the poorest potty control into the smallest volume of water,” she says
Kiddie pools also run warmer than the big pool, because shallow water heats up fast—and bacteria thrive in warmer water. The kids splashing in it are likely the most contaminated people at the pool and the most vulnerable
Swim diapers don’t solve the problem either since they leak, Reynolds says. By the time you notice, the pool already has whatever the diaper was holding
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“When I lecture on this in my class, students will come up to me and say, ‘I’m never swimming again,'” Reynolds says. “That’s not my intent.”
Instead, she wants parents to make a few simple habits part of every pool day. Build regular bathroom breaks into the day, she suggests, and wash little hands with soap—not a quick swish in the pool. Change diapers away from the water. And teach kids not to drink from the pool or treat splash-pad spouts like drinking fountains
You get back in the water too soon after being sick
Feeling better after a bout of diarrhea doesn’t necessarily mean you’re no longer contagious. So how long should you wait before getting back in the pool? “The guideline is brutal,” Reynolds says. “It’s two weeks.”
That’s two weeks after your diarrhea stops—not two weeks after it starts, and not just until you feel better. The reason is Cryptosporidium, a parasite that can keep shedding in your stool for up to 14 days after your symptoms disappear. Even trickier, the diarrhea can seem to clear before flaring up again because the parasite is still reproducing in your gut
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Reynolds admits the recommendation is intentionally cautious and says if you knew for certain you had norovirus or E. coli, a week would probably be enough. But most people never find out exactly what made them sick, because doctors don’t routinely test for every cause of diarrhea. So the guidance assumes the worst
And it’s not just little kids who spread germs in pools. Reynolds says plenty of outbreaks have been traced back to competitive swimmers who didn’t want to miss an event. “They’ve been traveling, they have traveler’s diarrhea, and they’re like, ‘I can’t miss this competition,'” she says. “And they get everybody sick.”
She understands how hard the recommendation can be. Imagine saving for years for a family vacation, only to tell your child they can’t swim. But if you’re still contagious, getting back in the pool doesn’t just affect your family—it can make dozens of other people sick, too
