Swimming is an excellent form of exercise. But like many activities, swimming in a pool has its downside.
Despite attempts to disinfect the pool, some pathogens may still
lurk in the water. And research suggests that disinfectants may pose
their own health hazards.
Swimming in chlorinated pools, particularly indoor pools, might
put kids at higher risk for developing respiratory illnesses, including
asthma and hay fever.
In addition, there is evidence that disinfectant
by-products--formed when chlorinated water is mixed with microorganisms,
human body fluids, cosmetics, and sunscreen--can damage your DNA and
increase your risk of cancer.
This sounds rather alarming. Does it mean we should keep kids out of the pool?
Not necessarily. It depends on the pool.
And we should keep in mind: Most studies concern kids who swim regularly. A few visits to the wrong swimming pool are unlikely to cause health problems.
So there is reason is reason for concern, not panic, and parents shouldn't feel helpless about the potential risks.
Here is an overview of the latest research on swimming pools, pathogens, and disinfectants. At the end of the article I offer tips on how to minimize risks to your child.
Why swimming pools need to be disinfected
A pool full of humans is liable to contain all sorts of pathogens, and humans are only part of the problem.
Water may be tainted by other sources – organic material derived
from decaying leaves, bird droppings, fungi-infested rainwater, or dead
So disinfecting water is a good idea, and there are several ways
to go about it, including ultraviolet radiation and the treatment of
water with a copper-silver solution.
But chlorination is the most popular method. It's cheap and
relatively effective (Loret et al 2005). When used properly, it protects
swimmers from a wide range of dangerous pathogens, including
• E. coli, Rotavirus, Salmonella, and Shigella (each of which may cause gastrointestinal symptoms and, in some individuals, serious illness)
• Adenoviruses (which are linked with gastroenteritis, respiratory infections, eye infections, and other diseases)
• Pseudomonas aeruginosa (which can cause a variety of diseases, including pneumonia and urinary tract infections)
Before the introduction of effective vaccines, chlorination was
also one of the only ways to protect swimmers from diseases like polio
and hepatitis A.
But no disinfection method is 100% effective. Some pathogens, like the protozoan parasites Giardia and Cryptosporidium, can survive the chlorination process.
Others are destroyed but only after sitting in chlorinated water
for 20 minutes or more. If you are unlucky enough to be in the pool
immediately after an infected child defecates in the water, your chances
of contracting the disease is very high (Kababjian 1995).
And unfortunately, disposable swim diapers offer very little
protection. When researchers put them to the test, they found these
diapers released most parasite-sized micro-particles within 5 minutes of
hitting the water (Amburgey and Anderson 2011).
This might suggest that we’d all be better off swimming in
highly-chlorinated pools. But there are health risks associated with
chlorination, and these must be balanced against the risks of infection.
Chlorine is itself an irritant, which is why pool managers must limit
the amount of chlorine they add to the water. But that’s not the only
problem with disinfectants.
Chlorine and chlorine compounds can form harmful by-products when
they are mixed with other agents. Unfortunately, these other agents are
common in swimming pool water. Perspiration, urine, saliva, hair, skin
particles, feces--even cosmetics and sunscreens--all contribute to the
formation of disinfectant by-products, or DBPs.
So the typical, chlorinated swimming pool contains DBPs. These
can be absorbed through the skin and swallowed. Because the chemicals
vaporize into the air, they are also inhaled.
Why is this harmful?
Researchers are still trying to understand how the body reacts to chlorinated water and DBPs.
Like chlorine itself, some DBPs are known respiratory irritants.
Maybe long-term exposure to chlorinated water vapor causes inflammation
of the air passageways. Maybe it causes oxidative stress, damaging the
lungs (Weisel et al 2009).
It also seems that DBPs can damage the DNA.
In a recent study, researchers tested the effects of disinfected swimming pool water on mammalian DNA.
They prepared several solutions—each a different kind of
disinfectant mixed with water—and applied them to living mammal cells
(Liviac et al 2010).
The results were consistent with other studies (e.g., Woodruff et
al 2001). All mixtures induced more DNA damage than plain tap water.
DNA damage is worrying because it increases the risk of cancer.
And that’s borne out by research. In laboratory experiments, DBPs have
caused cancer in rats (McDonald and Komulainen 2005). And studies have
linked exposure to these DPBs with an increased risk of cancer in humans
(Richardson et al 2007).
So we have good theoretical reasons to be suspicious about chlorinated pool water.
What about practical observations? Are swimmers becoming ill?
Does swimming in chlorinated water increase your risk of allergies and respiratory disease?
Unfortunately, there isn't any clear answer to this question.
Several studies conducted in Belgium and the Netherlands have
reported higher risk of respiratory problems. For example, in one study,
kids exposed to chlorinated pools before the age of 2 years were more
likely to have developed asthma, respiratory allergies, and
bronchiolitis, an inflammation of the bronchioles (2010).
Other research has linked early childhood pool exposure to higher
rates of eczema, air passageway inflammation, and sensitization to dust
mites (Jacobs et al 2012; Voisin et al 2013).
And a study of more than 800 Belgian teenagers found that kids
who spent longer hours in chlorinated pools were more likely to suffer
from asthma, hay fever, and other allergies. There was no increased risk
of respiratory allergies among teens who swam in pools disinfection
with a copper-silver solution (Bernard et al 2009).
Such results sound worrying, but several larger
studies--conducted in Germany, Italy, Spain, and Britain--have failed to
find any links between swimming pool exposure and respiratory illness.
One of the most compelling is a longitudinal study tracking over
5700 British children from the age of 6 months. Researcher Laia
Font-Ribera and colleagues looked for evidence that frequent swimming
increased the risk of asthma. They found none. In fact, kids who swam
more experienced fewer respiratory symptoms over time (Font-Ribera et al
Why the conflicting evidence? Maybe the studies reporting
problems are in error. But it’s also possible that the risk differs by
None of these studies measured the quality of the pool water, and
we know that chlorine levels can vary greatly. Different countries set
different standards for disinfection. A swimming pool in the United
States might have ten times as much chlorine as a pool in Germany
(Weisel et al 2009).
Does that mean German pools are safer than American pools? Maybe. But nobody’s attempted to answer that question yet.
Indeed, I haven't seen any epidemiological studies that
measured the concentration of disinfectant in the swimming pool water,
let alone other factors, like the quality of poolside air.
Perhaps variation among swimming pools can explain why different
studies have reported different outcomes. Maybe the studies reporting no
effect concerned swimming pools with low levels of disinfectant--or
particularly good ventilation.
As I note above, the evidence is inconclusive. The research on DNA
and cancer is still in the early stages, and we need more information
before we can interpret epidemiological studies.
But meanwhile, concerned parents can follow these guidelines.
• If you can smell the chlorine in the pool environment, there’s too much of it. That’s
the rule of thumb offered by researchers Brent S. Rushall and Larry
Weisenthal. Tell your local pool manager about your concerns.
• If you frequently swim indoors, find a pool with good ventilation. That
means avoiding pools that recirculate air rather than replace it with
fresh air. It also means avoiding pools in rooms with low ceilings.
• Avoid swimming pools that don’t insist on cleanliness—including showers before swimming. As
noted above, perspiration and other body products mix with chlorine to
produce disinfection by-products. When people wash with soap and water
before entering the pool, they help minimize the generation of DBPs.
• Tell kids not to pee or spit in the pool. It isn’t just gross—it contributes to the creation of DBPs.
• Encourage your local pool manager to consider research-based alternatives to traditional chlorination.
According to the researchers who conducted the DNA study, the safest
approach to disinfection may be a combination treatment: UV irradiation
with supplemental chlorination (Liviac et al 2010).
• If you are responsible for a pool or hot tub, don’t skip the disinfection process. As
noted above, disinfection serves a crucial purpose. The answer isn’t to
stop disinfecting pools. The answer is to find ways to disinfect while
minimizing other health risks.
References: Swimming pools and health risks
Amburgey JE, and Anderson JB. 2011. Disposable swim diaper retention
of Cryptosporidium-sized particles on human subjects in a recreational
water setting. J Water Health. 9(4):653-8.
Bernard A, Nickmilder M, Voisin C, and Sardella A. 2009. Impact
of chlorinated swimming pool attendance on the respiratory health of
adolescents. Pediatrics. 124(4):1110-8.
Centers for Disease Control and Prevention (CDC). 2010.
Violations identified from routine swimming pool inspections--selected
states and counties, United States, 2008. MMWR Morb Mortal Wkly Rep.
Font-Ribera L, Villanueva CM, Nieuwenhuijsen MJ, Zock JP,
Kogevinas M, Henderson J. 2011. Swimming pool attendance, asthma,
allergies, and lung function in the Avon Longitudinal Study of Parents
and Children cohort.Am J Respir Crit Care Med. 183(5):582-8.
Jacobs JH, Fuertes E, Krop EJ, Spithoven J, Tromp P, and Heederik
DJ. 2012. Swimming pool attendance and respiratory symptoms and
allergies among Dutch children. Occup Environ Med. 69(11):823-30.
Kababjian RS. 1995. Disinfection of Public Pools and Management of Fecal Accidents. Journal of Environmental Health 58(1).
Liviac D, Wagner ED, Mitch WA, Altonji MJ, and Plewa MJ. 2010.
Genotoxicity of Water Concentrates from Recreational Pools after Various
Disinfection Methods Environ. Sci. Technol. 44 (9), pp 3527–3532
McDonald TA and Komulainen H. 2005. Carcinogenicity of the
chlorination disinfection by-product MX. J Environ Sci Health C Environ
Carcinog Ecotoxicol Rev. 23(2):163-214.
Richardson SD, Plewa MJ, Wagner ED, Schoeny R, and Demarini
DM.2007. Occurrence, genotoxicity, and carcinogenicity of regulated and
emerging disinfection by-products in drinking water: a review and
roadmap for research. Mutat Res. 636(1-3):178-242.
Voisin C, Sardella A, Marcucci F, and Bernard A. 2010. Infant
swimming in chlorinated pools and the risks of bronchiolitis, asthma and
allergy. Eur Respir J. 36(1):41-7.
Voisin C, Sardella A, Bernard A. 2013. Risks of new-onset
allergic sensitization and airway inflammation after early age swimming
in chlorinated pools. Int J Hyg Environ Health. pii:
Woodruff NW, Durant JL, Donhoffner LL, Penman BW, and Crespi CL.
2001. Human cell mutagenicity of chlorinated and unchlorinated water and
the disinfection byproduct
3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Mutat Res.