Urine-Chlorine Combination Is What Causes Swimmers’ Eyes to Turn Red

If you plan to go swimming this summer, pack some goggles. It turns out that it’s not chlorine that causes swimmers’ eyes to turn red. At least, not chlorine alone.

According to the the Healthy Swimming Program, a collaboration between the Centers for Disease Control and Prevention, the Water Quality and Health Council, and the National Swimming Pool Foundation, swimmers’ eyes go bloodshot as a result of the chemical compounds formed when chlorine reacts with human urine.

“When we go swimming and we complain that our eyes are red, it’s because swimmers have peed in the water,” said Michele Hlavsa, chief of the healthy swimming program. “The nitrogen in the urine combines with the chlorine and it forms what’s known as chloramine and it’s actually chloramine that causes the red eyes. It’s not the chlorine itself. It’s chlorine mixed with poop and sweat and a lot of other things we bring into the water with us.”

As gross and awful as red-eye now seems, it’s not even the worst part. Recent research shows that when chlorine reacts with two chemicals in urine — urea and uric acid — it creates two poisonous gases that can actually harm a person’s lungs, heart, and central nervous system.

Hlavsa said healthy pools don’t smell like chemicals. The key to clean, healthy water is proper filtration and water chemistry. It doesn’t matter if a pool has 100 gallons of water or 1,000,000, the same balance levels and chemical types are required. Only the quantity will vary in proportion to the amount of water. So if a pool reeks of chlorine, it’s a little dubious. The more a pool smells like chemicals — the stronger the smell of chlorine — the more filled with urine it likely is.

Now, this doesn’t mean people should avoid taking a dip. It just means that they’d be wise to be more clean. The CDC recommends swimmers shower before diving in, avoid eliminating in the water, refrain from swimming if they have recently suffered from diarrhea, and try not to swallow any of the pool water.

“We don’t want to scare people away from swimming,” said Hlavsa. “It’s just about doing it in a healthier and safer way. We go biking and we wear helmets. We go in the car and we put our seatbelts on. We’re just saying, this is a healthier way to swim.”

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