Pool chlorine can cause red eyes, dry or itchy skin, breathing irritation and other side effects, but most of these come from what forms when chlorine reacts with sweat, pee and other material swimmers bring into the water. Those disinfection byproducts, including chloramines (also called combined chlorine), are behind the sting and the “chlorine” smell most swimmers know. Chlorine still does an important job by killing many germs, so the goal is to keep byproducts low.
Below are the 7 health effects people ask about most, who is most affected and how to lower each one. Swimming itself remains one of the best low-impact ways to stay active, so none of this is a reason to stay out of the pool.
This article is general information, not medical advice. Talk with your doctor about any health condition that affects how you swim.
Why does pool chlorine cause health problems?
Most side effects trace back to chloramines. According to the CDC’s guidance on chloramines and pool operation, chlorine reacts with pee, poop, sweat and dirt from swimmers to form chloramines. Chloramines release gas into the air, and because the gas is heavier than air, it settles just above the water where swimmers breathe. CDC says the buildup is worse indoors, especially in winter, when pools limit fresh air to save on heating.
For more on the chemistry, read what causes pool chlorine smell and how to get rid of it and What Are Disinfection Byproducts (DBPs) in Pools, and Are They Harmful?
1. Can pool chlorine cause red, itchy eyes?
Yes, and chloramines are the usual cause. The CDC’s page on preventing eye irritation from pool chemicals explains that chlorine combines with sweat and pee to form chloramines, which can turn into gas and irritate the eyes and lungs. Red, itchy eyes after a swim are one of the most common signs. CDC’s advice is to shower before swimming, use the toilet first, never pee in the water and tell the pool operator about strong chemical smells.
2. Why does chlorine make your skin dry and itchy?
Chlorinated water can dry out and irritate skin. The American College of Allergy, Asthma and Immunology (ACAAI) says skin reactions after swimming are usually irritant dermatitis, and that chlorine is drying to the skin and can irritate existing dermatitis. People with eczema or sensitive skin tend to notice it most. ACAAI recommends rinsing affected skin with clean water to remove any remaining irritant.
For practical skin care tips, see our guides to chlorine rash and sensitivity and preventing eczema flare-ups from pool chlorine.
3. Can pool chlorine affect your breathing or asthma?
Chloramines in pool air can irritate the nose, throat and lungs, according to CDC, and people with asthma may notice it first at poorly ventilated indoor pools. That does not mean people with asthma should avoid swimming. A 2013 Cochrane review of 8 trials found that swimming training did not worsen asthma control in children and teens with stable asthma, and it improved their fitness and lung function.
Read more in Can You Swim With Asthma or Allergies? and Pool Chlorine and Kids: What Parents Should Know.
4. Are competitive swimmers and lifeguards more affected?
People who spend the most hours in indoor pool air get the most exposure, which is why swim team season can mean more red eyes, coughing and dry skin. CDC notes that chloramines affect swimmers, spectators and pool staff. Research on young swimmers is mixed:
- A 2003 Belgian study of 1,881 schoolchildren (Bernard and colleagues) found that asthma was more common in children who had spent more total time at indoor chlorinated pools. The authors called for more research to test the link.
- A larger 2011 study of 5,738 British children (Font-Ribera and colleagues) found that swimming did not increase the risk of asthma or allergic symptoms, and children who swam the most had better lung function.
Elite swimmers report asthma more often than the general public; see why so many elite swimmers have asthma. Coaches and parents can help by asking for good ventilation, enforcing pre-swim showers and reporting strong chemical smells to the pool operator.
5. Can you get sick from germs chlorine doesn’t kill quickly?
Yes. Chlorine kills many germs, but some survive much longer. CDC’s report on outbreaks associated with treated recreational water from 2015 to 2019 (MMWR, 2021) counted 208 outbreaks and at least 3,646 cases. Cryptosporidium, a parasite that causes stomach illness, caused 76 of those outbreaks (49% of outbreaks with a confirmed cause) and 2,492 cases. CDC describes Crypto as extremely tolerant to chlorine: it can survive more than 7 days in water with 1 ppm free chlorine.
The CDC’s page about Crypto infections says the most common symptom is watery diarrhea, which usually starts 2 to 10 days after infection and lasts 1 to 2 weeks. To lower your risk, stay out of the water when you have diarrhea, try not to swallow pool water and take kids on bathroom breaks every hour, as CDC recommends in its tips for keeping kids healthy at the pool.
Many aquatic facilities add a supplemental system for this reason. In a 2014 University of Colorado Boulder lab study, the Clear Comfort system reduced chlorine-resistant Crypto by up to 99.99% (4-log) in under 60 minutes under lab conditions.
6. Do pool disinfection byproducts raise cancer risk?
The risk appears small for most swimmers and higher for people with heavy exposure. A 2023 health risk assessment prepared for New Zealand’s National Public Health Service noted that human data for some pool byproducts are inconclusive. One study it reviewed, covering 19 indoor pools in Budapest, estimated an added lifetime risk from one common byproduct of more than 1 in a million for recreational swimmers and more than 1 in 100,000 for elite swimmers and pool staff. The assessment still concluded that the total cancer risk from pool byproducts should not be considered negligible and that pools should minimize exposure without weakening disinfection. Swimming is also physical activity, and the CDC says being physically active lowers your risk for at least eight types of cancer.
For the full evidence, read Can Pool Disinfection Byproducts Raise Your Cancer Risk?
7. Is it safe to swim in a chlorinated pool while pregnant?
The largest study found no added risk. In the Danish National Birth Cohort study of 74,486 pregnancies (Juhl and colleagues, Epidemiology, 2010), women who swam had a slightly lower risk of preterm birth and birth defects than women who did not exercise, and the authors concluded the data “do not indicate that swimming in pool water is associated with adverse reproductive outcomes.”
A smaller 2019 U.S. study of 1,033 women in New Hampshire (Salas and colleagues, Environment International) found no link between swimming and birth weight or length. It did find small differences in head size and cord blood cells among regular swimmers, and the authors called for longer-term studies. Pregnant swimmers can talk with their doctor and choose well-maintained, well-ventilated pools.
How can you lower your exposure to pool chlorine byproducts?
For swimmers, CDC recommends these habits:
- Shower or rinse off before you swim. This removes sweat, lotion and dirt that react with chlorine. Read about pool etiquette and showering in the U.S. and Europe.
- Use the restroom first and never pee in the pool. See what happens when you pee in the pool.
- Wear a bathing cap to keep hair and scalp oils out of the water.
- Speak up about strong chemical smells. A strong “chlorine” smell usually means chloramines are building up.
For pool owners and operators, CDC’s chloramine guidance recommends measuring combined chlorine (total chlorine minus free chlorine), superchlorinating when combined chlorine is too high, bringing fresh air across the water’s surface at indoor pools and using supplemental systems that break down chloramines.
How does a low-chlorine pool help?
Clear Comfort’s hydroxyl-based AOP is a supplemental system that destroys contaminants in the water so a pool can run low-chlorine. Hydroxyl-based AOP still works alongside a low chlorine residual. In residential pools, the typical free chlorine range with hydroxyl-based AOP is 0.5 to 1.5 ppm, and system maintenance is an annual cartridge exchange that takes approximately 1 to 5 minutes per year.
At aquatic facilities, Clear Comfort case studies have reported 50% to 90% reductions in chloramines and other disinfection byproducts, depending on the facility. Two examples:
- YMCA pool (2015): lab testing at the University of Colorado Boulder found 84.8% lower levels of one major group of disinfection byproducts after Clear Comfort was added, according to the YMCA case study (case-specific result).
- JCC MetroWest, New Jersey (2016 to 2017): the indoor pool lowered free chlorine from 2.0 to 3.0 ppm to 1.0 to 1.5 ppm and cut total chemical cost by 41% over three quarters, according to the JCC case study (case-specific result, not a guarantee).
Salt water pools are a different approach: a salt chlorine generator makes chlorine from dissolved salt, so the pool still runs on chlorine. See how the two compare in Salt Water vs Clear Comfort AOP.
Frequently asked questions
Is pool chlorine bad for your health?
Chlorine in a well-run pool is an important defense against many germs. Most side effects, such as red eyes, itchy skin and breathing irritation, come from chloramines and other byproducts that form when chlorine reacts with sweat and pee. Showering before swimming and keeping byproducts low reduces those effects.
Why do my eyes sting after swimming in a chlorinated pool?
Stinging, red eyes usually come from chloramines. CDC explains that chlorine combines with sweat and pee to form chloramines, which can turn into gas and irritate the eyes and lungs. Showering first, never peeing in the pool and good pool maintenance all help.
Is it safe to swim with asthma?
Most people with well-controlled asthma can swim. A 2013 Cochrane review found swimming training did not worsen asthma control in children and teens with stable asthma, and it improved fitness and lung function. Poorly ventilated indoor pools with a strong chemical smell are the main thing to avoid.
Does chlorine kill all germs in a pool?
Chlorine kills many germs, but Cryptosporidium can survive more than 7 days in water with 1 ppm free chlorine, according to CDC. Crypto caused 76 outbreaks linked to pools and other treated recreational water from 2015 to 2019. Staying out of the water with diarrhea and not swallowing pool water lower the risk.
Is it safe to swim in a chlorinated pool while pregnant?
A Danish study of 74,486 pregnancies found no added risk from swimming, and swimmers had a slightly lower risk of preterm birth than women who did not exercise. A smaller 2019 U.S. study called for longer-term research. Talk with your doctor and choose a well-maintained, well-ventilated pool.
Do salt water pools avoid chlorine?
No. A salt water pool uses a salt chlorine generator to make chlorine from dissolved salt, so the pool still runs on chlorine and can still form chloramines. A supplemental system such as Clear Comfort’s hydroxyl-based AOP is what lets a pool run low-chlorine.
Want a low-chlorine pool at home? See how Clear Comfort works for residential pools and spas.
