A recent Facebook post warned that peeing in swimming pools is not only gross, but also causes dangerous chemicals to form that can hurt both the heart and lungs.

“Urinating in a pool is dangerous for you heart? Urine and chlorine create dangerous chemicals when combined. One of those chemicals is classified as a chemical warfare agent and can damage your heart and lungs,” reads the post that was shared more than 400 times a week, according to USA Today.

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When the uric acid in urine combines with chlorine in swimming pools it creates toxic chemicals like cyanogen chloride and trichloramine. A 2014 study published in the journal Environmental Science and Technology said that cyanogen chloride “can affect multiple organs, including the lungs, heart and central nervous system via inhalation,” and trichloramine “has been associated with acute lung injury in accidental, occupational or recreational exposures to chlorine-based disinfectants.”

Cyanogen chloride is a highly toxic form of cyanide, which is used as a chemical weapon agent. Ernst R. Blatchley, a professor in environmental engineering at Purdue University, says that both chemical compounds escape from liquid into the air and can cause damage to the respiratory system, as well as other organs.

“It is possible to see effects in other organs if these chemicals are transferred from the lungs into the blood supply, then circulated,” Blatchley told USA Today. “The potential exists for acute effects and chronic effects. Both have been documented in swimmers.” The experts recommended showering before getting in a pool and reiterated that people should leave the water to pee.

It’s important to avoid high-traffic pools where hygiene is not properly regulated, as well as outdoor pools where the wind can carry those chemicals into the air. Limit swimming in those pools to 30 minutes or less.

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