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Hidden Toxins in Your Swimming Pool

Updated: Aug 9, 2021

Ever notice the “chlorine” smell that often accompanies you after a trip to your neighborhood pool? That smell isn’t actually chlorine. It’s the byproduct of a chemical reaction between chlorine and urine- a volatile compound called trichloramine.

And trichloramine isn’t the only byproduct chlorine creates when you jump into a pool. Other, more harmful disinfection by-products (DBPs), have been linked to respiratory disorders, bladder cancer, and oxidative stress.

Here’s how to keep yourself safe from chlorine by-products this summer.

swimming pool, toxins, chlorine

Chlorine 101:

Chlorine is one of the most commonly used industrial chemicals today. It is used in everything from solvents, to bleaching agents in paper production, to sanitizing industrial waste and sewage, to killing bacteria in drinking water and swimming pools. But let us not forget that it’s the same “chlorine” that was used as a chemical weapon during both World Wars that killed over 91,000 people.

While chlorine gas as a chemical weapon is in very, very high concentrations, it is still the same toxin used in your neighborhood swimming pool. Chlorine works so well as a disinfectant because it reacts with and disrupts the function of biomolecules needed by microbes and other organisms to survive. This is obviously a very toxic process. And, unsurprisingly, there are numerous detrimental health effects for those people who spend a lot of time in the pool.

But these chlorine side effects are largely caused by what happens during the pool filtration cycle when chlorine is introduced to particles of urine, sweat, sunscreen, and dirt from the pool. The resulting chemical reaction produces harmful disinfection by-products (DBPs).

How does pool filtration create DBPs?

Most pools have a gutter system that withdraws the water to filter the water through the treatment system outside of the pool. This process often involves a sand filter, re-chlorination, and a pH adjustment. But in some cases, UV radiation is used as a further disinfectant. When UV light is used, it is applied after filtration and before chlorine injection and pH adjustment.

The problem with using UV radiation as a disinfectant is that it breaks nitrogen-chlorine bonds in some DBPs. This produces free radicals that work to form increasingly harmful DBPs such as cyanogen chloride, a toxic molecule that can attack respiratory organs. So while UV systems are great for improving water quality, they also create dangerous chemicals.

Further, it is estimated that only about 1% of pool water is lost and replaced per day. That means it takes around 100 days for most of the water in a pool to be replaced. For those 100 days, harmful DBPs are accumulating and waiting for their next victim to jump in.

DMPs 101:

DMPs are the product of a reaction between any foreign particle reacting to chlorine in the pool or UV light in the filtration process. There are three main categories of DMPs:

  1. The first category is loose dirt. This first is easily swept away by pool water after someone jumps in.

  2. The second category is sweat. Sweat could have been accumulated before entering the pool or once in the pool.

  3. The third category is urine. Researchers estimate that 30 to 80 mL of urine is added to a pool for every person. Further, for elite swimmers, that number is likely much higher. Urine contributes to around 30% of DBP formation. Urine’s byproduct in reaction to chlorine is trichloramine.

There are hundreds of different kinds of DBPs in pools. These range from harmless to potentially very dangerous. The most common DBPs are trihalomethanes, this category includes trichloromethane (more commonly known as chloroform), haloacetic acids, and chloramines (especially trichloramine).

Most of the DBPs are volatile, meaning in the warm air of an indoor pool, they will end up in the air after a chemical reaction occurs. When DBPs enter the air, they become much more dangerous, as they are not absorbed very well through the skin. Trichloramine, the DBP associated with urine, is the most volatile and has been linked to numerous adverse health effects in humans of all ages. Trichloramine and other volatile DBPs are likely the key contributors to respiratory problems in swimmers.

One study examining DBPs in swimming pools found previously unknown DBPs in the pool that are extremely harmful to humans. The researchers found high levels of halobenzoquinones, which are derived from commonly available lotions, sunscreens, and other personal care products that contain phenyl. The by-product of this chemical is benzoquinone- a known carcinogen. But, after reviewing cell-based assays, the researchers found that halobenzoquinones are even harmful. Halobenzoquinones produce a much higher amount of reactive oxygen species in cells, which results in DNA and protein damage.

If you’re wondering if these harmful chemicals are absorbed into your body after swimming, the answer is yes. A recent study examined just how many DBPs are taken inside the body after a swim. Unsurprisingly, the researchers found that after a 40-minute swim, levels of all the tested DBPs had increased. The levels were even higher after a swim in a pool with lots of urine.

Harmful effects of DBPs:

The long-term effects of chlorine and DBPs on swimmers are relatively unknown. But the CDC has cited negative effects of chlorine over-exposure on a person’s health- these include blurred vision, respiratory issues, and asthma. A 2003 study by the CDC found that 54% of all swimming facilities were in violation of improper chlorination, filtration system irregularities, and faulty water disinfection practices.

Several studies have also suggested that adults and children react differently to toxins in pool water. Children are at an increased risk of developing allergies or asthma. While adults are more likely to develop bladder and rectal cancer and are at an increased risk of coronary heart disease.

The clearest example of chlorine and DBP over-exposure can be seen in elite swimmers, as they spend up to hours per day in a chlorine-filled swimming pool. The most obvious side-effect of chlorine and DBP exposure are respiratory problems.

Many elite swimmers also have significantly higher rates of allergy sensitivities. This is due to chlorine and DBPs that tend to hover in the air above the pool, where they are then inhaled. When you inhale chlorine and DBPs, the airway is damaged, promoting the development of allergic sensitivities.

In a study on rats that trained at the same rate as elite swimmers, researchers discovered that over the course of 12 weeks, many of the rats developed health problems. Throughout the study, many of the rats developed bloody noses and eyes, hair loss, and dry skin. Moreover, through a metabolomics analysis, metabolic stress caused by DBPs and chlorine was discovered in the heart, liver, spleen, lungs, and kidneys.

How to avoid chlorine and DBP toxicity:

We don’t want to ruin all of your summer fun and scare you away from a nice, relaxing day at the pool. So we have compiled a list of things you can do to limit reaction to DBPs and chlorine:

  • Avoid lathering on lotion before the pool

  • Don’t spend too much time in a warm, indoor pool

  • Use organic skincare products to avoid the promotion of volatile DBPs

  • Take a quick shower or rinse off before getting in the pool

  • Shower after a swim

  • Opt for saltwater pools if given the option

  • Drink lots of water before you swim


However, for some individuals, lifestyle changes like showering before the pool will not be enough to prevent chlorine or DBP toxicity. There are genetic variations that limit or slow the detoxification process in the body, meaning they stay in the body for longer and have more time to cause adverse health effects.

For people with such genetic variation, proper supplementation and dietary changes are necessary to avoid bad side effects from too much time in the pool. For more information about genetic testing or supplementation, click here to contact us!

The Johnson Center for Health services patients in-person in our Blacksburg and Virginia Beach / Norfolk locations. We also offer telemedicine for residents of Virginia and North Carolina!


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