No, it’s likely not chlorine you’re smelling when you walk by the pool. That aroma is actually from a chemical reaction happening between the chlorine and bodily fluids, most notably urine. It’s a hard truth to confront during the sweltering summer heat, but science can explain why it happens.
“People are peeing in the swimming pool, and we have the chemistry to prove it,” VidCon founder, author, social media content creator and science communicator Hank Green told millions of followers on his YouTube channel SciShow.
“That’s not chlorine that creates the distinctive pool smell,” Green continued. “That’s chemicals that form when chlorine reacts with pee, sweat and body oils, but mostly pee.”
According to a 2019 survey by Sachs Media Group, just over half of Americans surveyed said they’ve used a pool as a communal bathtub at least once. Nearly a quarter said they they’ve substituted a shower with a quick dip in the pool. Total number who have urinated in the pool as an adult? Two in 5 (40%).
“Researchers mixed chlorine with uric acid, a compound found in both sweat and urine, but by far in more concentration in urine,” he said. “The result (was) trichloramine and cyanogen chloride, which contribute to the pool smell. But even worse, it can irritate your eyes and lungs.”
According to the National Center for Health Research, the health ramifications of swimming in water containing these dangerous chemical byproducts are still being studied.
One 2009 study discovered teenagers who swim in chlorinated pools are at higher risk of developing asthma or hay fever. Another study, in 2004, reported lung irritation in children who swam frequently. Multiple studies have reported higher rates of respiratory health problems in competitive swimmers. While none of these studies have directly linked trichloramine and cyanogen chloride to these health hazards, the national center said researchers continue to theorize these chemicals as potential suspects.
The Atlanta-based Centers for Disease Control and Prevention, however, has directly linked chloramines — the chemical byproducts of chlorine and body fluids — to eye, skin and respiratory irritation.
“So if you’re tired of getting all red eyed after a swim and your pool smells like chlorine, you now know what to blame,” Green said. “And that’s why chemists are asking people to please, please stop peeing in the pool.”
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