It's Pee, Not Just Chlorine, That Irritates Eyes in the Pool

Red eyes after a day of swimming has long been blamed on chlorine, but according to the Centers for Disease Control and Prevention, urine is the culprit. Tim Wimborne/Reuters

People have always assumed that chlorine was the chemical devil behind their red, irritated eyes after a dip in the pool. But the Centers for Disease Control and Prevention's (CDC) annual healthy swimming report says that isn't actually the case.

The true cause, it says, is nitrogen in urine binding to chlorine to form chloramine—a derivative of ammonia. "It's not the chlorine itself," Michele Hlavsa, chief of the CDC's healthy swimming program, told Today. "It's chlorine mixed with poop and sweat and a lot of other things we bring into the water with us." The compound can also make swimmers' noses run and cause them to cough.

And pools' "chlorine" smell isn't actually the chlorine either. The stronger a pool's scent, the more it is filled with pee, poop, sweat and dirt, says the CDC. "Healthy pools...don't have a strong chemical smell."

Chlorine is in pools not to deal with the pee but to kill harmful germs like E. coli. When urine is added in large quantities, tackling it becomes chlorine's full-time job, which allows germs to linger in the water.

"I just don't think this is on people's radars," Hlavsa told Today. "People think waterborne disease is something that happens outside the United States. But really, we have plenty of them here."

The CDC's report isn't meant to turn pools into ghost towns this summer, but to provide some tips for healthier visits. For instance, avoid opaque, smelly pools and take children to visit the bathroom every hour...for everyone's sake.

Happy swimming!