Swimming in water with too much chlorine can irritate your skin, sting your eyes, inflame your airways, and expose you to chemical byproducts that linger in your blood and breath long after you towel off. Most pool-goers have experienced mild versions of these effects on a normal swim day, but when chlorine levels climb well above the recommended range, the consequences can shift from annoying to genuinely harmful. The story goes deeper than redness and coughing, though, because chlorine in pool water reacts with organic matter to create an entire secondary cocktail of compounds your body absorbs through routes you might not expect.
What Happens to Your Skin
Chlorine is an oxidizer. That is how it kills bacteria, but it also strips the natural oils and lipids that form your skin’s protective barrier. At normal pool concentrations, this tends to leave you feeling dry and slightly tight after a swim. At elevated levels, the damage accelerates. Your skin can become visibly red, itchy, and flaky, sometimes within a single session. Prolonged or repeated exposure to high-chlorine water has been linked to irritant contact dermatitis, a condition where the skin barrier breaks down enough to trigger inflammation even without an allergic response.1Open Access Research Journal of Biology and Pharmacy. Chronic effects of swimming pool disinfectants on skin and hair
The mechanism is straightforward: chlorine reacts with proteins in your outer skin layer, degrading the stratum corneum, the thin sheet of dead cells that keeps moisture in and irritants out. Once that barrier weakens, water actually escapes from your skin faster, which is why chlorine-exposed skin often feels drier than skin that was never wet at all. Free residual chlorine in pool water has been shown to reduce the water-retaining properties of the stratum corneum, a finding especially relevant for anyone with sensitive or eczema-prone skin.2PubMed Central. Pooling the evidence: A review of swimming and atopic dermatitis
Hair takes a hit too. Chlorine strips the protective cuticle layer, leaving hair dry, brittle, and prone to that characteristic green tinge that comes from oxidized copper compounds in the water rather than from the chlorine itself. Swimmers who train frequently in poorly maintained pools often notice significant texture changes in their hair over the course of a season.
How Your Lungs React
The respiratory effects of high chlorine exposure can be divided into two very different categories: what happens in a sudden, accidental spike, and what happens over months or years of repeated lower-level exposure. Both matter, and both have solid research behind them.
Acute Exposure
When something goes wrong with a pool’s chemical dosing system, chlorine gas can be released in concentrations far above what anyone should breathe. A case study of a swimming pool accident documented a range of serious respiratory injuries among the 22 patients treated. Roughly one in five developed pneumonia, a similar proportion had pulmonary edema (fluid in the lungs), and others showed inflammation of the bronchial tubes. Three months after the accident, nearly half of the patients who returned for follow-up still had measurable obstructive ventilation defects or small airway dysfunction.3PubMed. Acute chlorine poisoning caused by an accident at a swimming pool In other words, a single high-dose exposure can cause lung damage that persists for months. The structural changes that follow high-level chlorine inhalation are still not fully understood, even though the acute effects are well documented.4PubMed Central. Quantitative assessment of chlorine gas inhalation injury based on endoscopic OCT and spectral encoded interferometric microscope imaging with deep learning
Chronic Exposure in Competitive Swimmers
You do not need an accident to develop respiratory problems from chlorinated pools. Competitive swimmers spend hours a day breathing heavily just above the water’s surface, right where chloramine concentrations are highest. A survey of 738 competitive swimmers found remarkably high rates of respiratory symptoms: sneezing in about 45%, breathing difficulty in roughly 39%, coughing in 36%, and wheezing in about 26%. Nearly one in five swimmers competing at the international level reported having asthma. When researchers tested bronchial responsiveness, over 60% of competitive swimmers showed increased airway reactivity compared to just 12.5% of non-swimming athletes.5European Respiratory Journal. Occupational asthma caused by chloramines in indoor swimming-pool air
A narrative review of the broader literature reinforced this pattern, noting that the combination of intense endurance training over long periods and suboptimal air quality around pools contributes to rhinitis, asthma, and bronchial hyperresponsiveness in athletes. Elevated blood levels of a specific antibody marker linked to allergic sensitization have been found in swimmers with long-term chlorine exposure, suggesting the immune system itself may be shifting in response.6PubMed Central. Pulmonary function in swimmers exposed to disinfection by-products: a narrative review
The Problem Is Not Just Chlorine
Here is where the story gets more complicated than most people realize. The chemical that stings your eyes and makes you cough at an indoor pool is usually not chlorine itself. It is a family of compounds called chloramines, formed when chlorine reacts with nitrogen-containing organic matter brought in by swimmers: sweat, urine, skin cells, and personal care products. The more “stuff” swimmers bring into the water, the more chloramines form, even if the chlorine level itself is within normal range.
Chloramines are toxic compounds created during the use of bleach-based disinfectants. The active ingredients, hypochlorous acid and the hypochlorite ion, react with ammonia and organic nitrogen to produce mono-, di-, and trichloramine. These compounds readily transfer from the water into the air, which is why the smell is strongest right at the pool surface and in enclosed, poorly ventilated spaces.7PubMed. Elevated levels of chloramines and chlorine detected near an indoor sports complex Trichloramine in particular is volatile and has been specifically linked to swimming-pool-associated asthma.8PubMed. Drowning in disinfection byproducts? Assessing swimming pool water
This is why a pool that “smells like chlorine” is actually a pool with a chloramine problem, often caused by insufficient free chlorine to fully oxidize contaminants, or by a heavy bather load. A well-maintained pool with adequate chlorine and good ventilation should barely smell at all. Some facilities have started using active air stripping systems that promote the transfer of volatile compounds like trichloramine out of the water and vent them directly outside, rather than letting them accumulate in the breathing zone above the pool.9PubMed. Active air stripping and direct point exhaust of trichloramine (NCl(3)) from indoor pools
Disinfection Byproducts and How They Get Into Your Body
Beyond chloramines, chlorinated pool water contains a broader class of chemicals called disinfection byproducts, or DBPs. The most studied group is trihalomethanes, with chloroform being the most abundant in most pools. Others include halogenated acetic acids, haloketones, and halogenated derivatives of UV sunscreen compounds, some of which show endocrine-disrupting effects.8PubMed. Drowning in disinfection byproducts? Assessing swimming pool water Higher chlorine levels generally mean more DBPs, especially when combined with a heavy organic load from swimmers.
What surprises most people is how these compounds enter your body. Swallowing pool water is the obvious route, but it is actually the least important one for trihalomethanes. The two main exposure pathways are breathing and skin absorption.10PubMed. Regulation, formation, exposure, and treatment of disinfection by-products (DBPs) in swimming pool waters: A critical review An experiment that measured blood chloroform levels in swimmers with and without scuba tanks, plus non-swimmers who just walked around the pool deck, helped tease apart these routes. Swimmers breathing pool air had blood chloroform concentrations roughly three times higher than swimmers breathing from scuba tanks, and the scuba-tank swimmers had levels similar to the people who never entered the water at all. The conclusion: about two-thirds of the trihalomethane burden comes from breathing the air above the pool, and roughly one-third comes through the skin.11International Journal of Hygiene and Environmental Health. Pathways of trihalomethane uptake in swimming pools
This finding has practical implications. It means that spending time at an indoor pool without swimming, as a lifeguard, coach, or spectator, still exposes you to meaningful levels of these compounds through the air. It also means that better ventilation, not just better water treatment, is critical to reducing exposure.
What High Chlorine Does to Your Teeth
This one catches people off guard. Improperly maintained chlorination systems can cause pool water to become highly acidic, and acidic water dissolves tooth enamel. A study of swimmers at a gas-chlorinated pool found that 39% of swim team members reported symptoms compatible with dental enamel erosion, compared to 12% of casual swimmers and just 3% of non-swimmers. When investigators tested the pool water, they found a pH of 2.7, roughly 100,000 times more acidic than the recommended range of 7.2 to 8.0.12PubMed. Erosion of dental enamel among competitive swimmers at a gas-chlorinated swimming pool
A pH that low is extreme and reflects a serious failure in pool management, but lesser degrees of acidity are more common than you might think, particularly in smaller or privately maintained pools where monitoring is inconsistent. The damage is irreversible: enamel does not grow back. Affected teeth become sensitive, discolored, and more vulnerable to decay. Research into protective measures has shown that fluoride treatments, including fluoridated milk rinses, can offer some protection against enamel erosion from low-pH pool water, but preventing the acidity in the first place is obviously the better strategy.13PubMed. Effects of tannin-fluoride and milk-fluoride mixture on human enamel erosion from inappropriately chlorinated pool water
If You Already Have Eczema or Asthma
People with atopic dermatitis (eczema) face a genuine dilemma with chlorinated pools. On one hand, chlorine’s antiseptic properties may actually reduce the bacterial colonization that worsens eczema flares, similar to the way dilute bleach baths are used therapeutically. On the other hand, chlorine dries out already-compromised skin and can trigger irritant or allergic contact dermatitis.2PubMed Central. Pooling the evidence: A review of swimming and atopic dermatitis The evidence is genuinely mixed, and the practical answer probably depends on severity: someone with mild, well-controlled eczema may do fine with a rinse and heavy moisturizer afterward, while someone in an active flare could see rapid worsening.
For asthma, the picture is clearer and less encouraging. Indoor pools with poor ventilation and high chloramine levels are a documented trigger for bronchospasm. If you already have reactive airways, swimming in a high-chlorine indoor pool is a setup for trouble. Outdoor pools are somewhat safer in this regard because volatile irritants disperse into the open air rather than accumulating in an enclosed space. Regardless of setting, anyone with asthma who notices worsening symptoms around pools should take that seriously. The respiratory effects of chloramine exposure have been linked to occupational asthma in pool workers, not just in swimmers.5European Respiratory Journal. Occupational asthma caused by chloramines in indoor swimming-pool air
Genotoxic Effects and the Long-Term Question
The most unsettling research on pool chemistry involves genotoxicity, meaning the potential for pool water byproducts to damage DNA. Lab studies have consistently found that all disinfected recreational pool water samples cause more genomic DNA damage than the source tap water used to fill them.14PubMed. Genotoxicity of water concentrates from recreational pools after various disinfection methods The genotoxic activity tends to concentrate in the low-molecular-weight chemical fraction of pool water.15PubMed. Swimming pool water–fractionation and genotoxicological characterization of organic constituents
Does that translate to real health effects in actual swimmers? A study measured biomarkers in people before and after a 40-minute swim in a chlorinated indoor pool. After swimming, markers of genotoxic damage increased: the frequency of micronucleated lymphocytes (a type of DNA damage indicator in blood cells) rose in proportion to how much brominated trihalomethane each swimmer exhaled. Urine mutagenicity also increased significantly after swimming, particularly in association with higher bromoform exposure.16PubMed Central. Genotoxic effects in swimmers exposed to disinfection by-products in indoor swimming pools
Before you swear off swimming forever, some context. The genotoxic changes measured in these studies are biomarkers, meaning they indicate cellular-level damage but do not by themselves prove that swimming causes cancer. The connection between pool DBPs and bladder cancer has been explored in epidemiological research, with some researchers hypothesizing that trihalomethanes absorbed through the skin and lungs reach the bladder and are activated there into mutagenic forms.8PubMed. Drowning in disinfection byproducts? Assessing swimming pool water But the overall evidence is not strong enough to conclude that recreational swimming poses a meaningful cancer risk. The cardiovascular and fitness benefits of swimming are well established, and for most people those benefits likely outweigh the theoretical DBP exposure risk. The concern is more pressing for competitive swimmers and pool workers with years of heavy, daily exposure, and for facilities where chlorine management is poor.
Your Skin’s Microbial Ecosystem
Your skin hosts a complex community of microorganisms that contributes to immune defense and skin health. Chlorine exposure disrupts this ecosystem. A scoping review examining swimming and the human microbiome found that training volume and intensity affected the composition, richness, and diversity of the swimmer’s microbiome, particularly the non-core (peripheral) microbial communities. The disruption is not just an academic curiosity: shifts in the skin microbiome have been linked to increased susceptibility to skin infections and inflammation, including acne, among swimmers.17PubMed Central. Swimming and the human microbiome at the intersection of sports, clinical, and environmental sciences: A scoping review of the literature
This is an area where research is still early, but the practical takeaway aligns with what dermatologists already recommend: rinse thoroughly after swimming, apply moisturizer to restore the skin barrier, and pay attention to any new or worsening skin issues if you swim frequently. For high-chlorine exposure specifically, the microbiome disruption would be expected to be more severe and faster-acting, though no study has yet isolated the dose-response relationship for skin microbiota at different chlorine concentrations.
Pregnancy and Pool Exposure
Pregnant swimmers sometimes wonder whether pool chemicals could affect fetal development. One study looked at maternal swimming pool exposure during pregnancy and found that among women who swam, the duration of swimming was inversely related to the baby’s head circumference at birth: each increase in swimming duration was associated with a small decrease in head circumference. No associations were found with birth weight, birth length, or DNA methylation changes.18PubMed Central. Maternal swimming pool exposure during pregnancy in relation to birth outcomes and cord blood DNA methylation among private well users
The researchers themselves emphasized that the finding was modest and that longer-term studies are needed. It is worth noting that this study looked at normal pool exposure, not specifically high-chlorine conditions, so any effect from elevated chlorine would be a separate and still-unanswered question. Current medical guidance generally considers recreational swimming safe during pregnancy, but the DBP exposure question remains an open area of investigation. If you are pregnant and concerned, swimming in a well-maintained outdoor pool with good water chemistry is likely the lowest-risk option.
Indoor Versus Outdoor Pools
The distinction between indoor and outdoor swimming environments keeps surfacing across different health effects, and for good reason. Indoor pools concentrate volatile chemicals in enclosed air. Trichloramine, chloroform, and other volatile DBPs that would simply blow away at an outdoor facility instead accumulate in the breathing zone of an indoor pool hall. This is why respiratory symptoms, genotoxic biomarker changes, and that sharp chemical smell are all more pronounced indoors.
Ventilation design matters enormously. Older facilities with recirculated air and low ceiling heights tend to have the worst air quality. Modern aquatic centers increasingly use dedicated air-handling systems designed to sweep contaminated air away from the pool surface and exhaust it outside. Some facilities have adopted active air stripping technology that forces volatile compounds out of the water and vents them directly to the exterior.9PubMed. Active air stripping and direct point exhaust of trichloramine (NCl(3)) from indoor pools If you are choosing between two indoor pools and one of them has noticeably less chemical smell, that is a genuine signal about air quality, not just aesthetics.
Outdoor pools still produce DBPs in the water itself, but the open-air setting dramatically reduces inhalation exposure. Sunlight also breaks down some chlorine compounds, which is partly why outdoor pools require more frequent chlorine dosing but may paradoxically deliver lower peak exposures of volatile byproducts to swimmers. The tradeoff is UV-related skin exposure, which is a separate consideration entirely, but from a pure chlorine-chemistry standpoint, outdoor swimming is easier on your lungs.
How to Tell If Chlorine Levels Are Too High
Most public pools in the United States target a free chlorine level between 1 and 3 parts per million, with pH between 7.2 and 7.8. Your body gives you useful signals when something is off. Stinging eyes, a strong chemical smell, and skin that reddens quickly are all signs of either elevated chlorine, elevated chloramines, or low pH. You cannot distinguish these causes by feel alone, but any of them means the water chemistry is not right.
Inexpensive test strips are available at pool supply stores and can measure free chlorine and pH in seconds. If you swim regularly at a facility and have ever wondered about the water quality, testing it yourself once or twice will tell you more than any amount of trusting the management. For your own backyard pool, testing before every swim is standard practice, and keeping chlorine within range while maintaining proper pH protects both your health and your pool surfaces. A pool with high chlorine but proper pH is less corrosive than one with moderate chlorine and dangerously low pH, as the dental enamel research dramatically illustrates.
If you do swim in water that turns out to have been over-chlorinated, the single most effective thing you can do afterward is rinse your entire body and hair with fresh water as soon as possible, then apply a moisturizer. For your eyes, plain saline drops help. For any respiratory irritation that persists beyond a few hours, or any wheeze or chest tightness, it is worth seeing a doctor, because the case literature on chlorine inhalation injuries shows that what feels like a minor annoyance can sometimes involve more significant airway inflammation underneath.