Urine mixes with chlorine in swimming pool water to create two chemical byproducts that can cause potential health problems.

Peeing in the swimming pool is not only unhygienic, it is also unhealthy, researchers of a new study found. According to a Healthy Pools survey, one in every five Americans (20 percent) admitted they've urinated in a swimming pool at least once. This astonishingly high number compelled researchers at Purdue and China Agricultural universities to look into what happens when urine combines with water containing chemicals like chlorine.

"We know that there are associations between some of these chemicals and adverse human health outcomes, so we're motivated to understand the chemistry behind their formation and decay," said Blatchley, a professor at the School of Civil Engineering and Division of Environmental and Ecological Engineering at Purdue University, according to The Atlantic.

An analysis revealed that two potentially dangerous chemical byproducts are formed. Uric acid in urine reacts with the chlorine to form cyanogen chloride and thrichloramine, two chemicals that are associated with health problems affecting the lungs, heart, central nervous system and other body organs. Researchers also found that when more uric acid was added to water already containing the two chemical compounds, the level of cyanogen chloride rose to dangerous levels.

Uric acid accounts for 24 to 68 percent of cyanogen chloride and 3 to 4 percent of thrichloramine found in swimming pool water, according to L.A. Times. Both these compounds contain nitrogen and since urine also contains nitrogen, there's bound to be a reaction. Nitrogen trichloramine (NC13) is a poisonous gas that can cause acute lung injury.

Uric acid is also present in sweat but in very small quantities. However, it is urinating in the swimming pool that poses a health threat, not sweating. Statistics show that a person leaves about 30 to 80 milliliters of urine behind each time one visits the pool. In fact, a previous study conducted during a national swimming competition found that NC13 levels doubled after one day of use.

Blatchley noted that the consequences can be all the more severe during swimming competitions and in big water parks where hundreds of people take a dip in a swimming pool at once. Generally chlorine in the water checks the rate at which cyanogen chloride is formed. It also contributes to decaying the compound faster. However, when many people are urinating in a pool at once, the chlorine content in the water gets depleted and cyanogen chloride sticks around for longer.

Many people are of the opinion that peeing in the pool is harmless. In fact, their assumptions grew even stronger when Olympic swimmers Michael Phelps and Ryan Lochte admitted to peeing in pools all the time in 2012.

"There's a lot of people in the swimming community who look up to these people and listen to what they have to say," Blatchley said, according to USA Today. "[Phelps and Lochte] are not chemists and shouldn't be making statements that are that false."

Urine in pools is not the only problem. A May 2013 CDC report revealed that feces (human poop) is frequently introduced into pool water by swimmers. 58 percent of the feces samples tested contained Escherichia coli, a bacterium that lives in the digestive tract of humans and other warm-blooded animals.

"Swimming is an excellent way to get the physical activity needed to stay healthy," said Michele Hlavsa, chief of CDC's Healthy Swimming Program. "However, pool users should be aware of how to prevent infections while swimming. Remember, chlorine and other disinfectants don't kill germs instantly. That's why it's important for swimmers to protect themselves by not swallowing the water they swim in and to protect others by keeping feces and germs out of the pool by taking a pre-swim shower and not swimming when ill with diarrhea."

Coming back to the topic of peeing in pools, not all types of urine are considered bad. A controversial study last year stated that cow urine actually has many health benefits. Reportedly, it offers a cure for around 70 to 80 incurable diseases like diabetes, Reuters reported at that time. However, since it's not cows but humans that are peeing in swimming pools, people should be more aware and stop peeing in pools.

The recent study was funded by Chinese Universities Scientific Fund, the National Natural Science Foundation of China and the National Swimming Pool Foundation. Findings were published in the American Chemical Society's journal Environmental Science & Technology