Urinating in swimming pools could lead to health problems.

Scientists found that compounds in urine mix with chlorine can cause chemicals that have been linked to respiratory effects in swimmers to form. They warned swimmers to stop the common practice after analysing samples.

"If swimmers avoided urinating in pools, then air and water quality would likely improve independent of other changes in water treatment or air circulation,” the scientists from China Agricultural University and Purdue University wrote in the journal Environmental Science & Technology.

In a series of laboratory experiments, the scientists combined water collected from swimming pools in China with mixtures meant to mimic the chemical composition of sweat and urine.

Chlorine, used to disinfect pools, reacts with many chemicals found in human sweat and urine.

Uric acid, found in urine, accounted for 24 to 68 percent (depending on temperature, water pH and chlorine condition) of the byproduct cyanogen chloride in the pool water samples. 

"Analysis of swimming pool water samples, combined with the results of experiments involving chlorination of uric acid, and chlorination of body fluid analog mixtures, indicated that uric acid chlorination may account for a large fraction of Cyanogen chloride formation in swimming pools,” the researchers say.

Cyanogen chloride can affect multiple organs, including the lungs, heart, and central nervous system via inhalation.

Exposure to trichloramine at pools has previously been linked to reduced lung function in adult swimmers, and itchy eyes, runny nose and voice loss in lifeguards.