Chloramines are compounds that form when chlorine in pool water combines with sweat, urine and other waste that swimmers bring into the water. They cause the strong “chlorine” smell at many indoor pools, and they can irritate the eyes, skin and lungs. Keeping chloramines low takes cleaner swimmers, steady water treatment and good air movement over the water.
What are chloramines?
Chloramines are a type of combined chlorine, a disinfection byproduct that forms when chlorine reacts with body waste in the water. CDC’s chloramine guidance for pool operators (reviewed June 2025) explains that chloramines form in the water and then move into the air above it, especially at indoor pools.
Pool test kits measure free chlorine (the chlorine still available to kill germs) and total chlorine. Combined chlorine, which is mostly chloramines, is total chlorine minus free chlorine. For more on the three readings, see free, combined and total chlorine: what’s the difference.
How do chloramines form in a pool?
Chloramines form when free chlorine reacts with nitrogen-containing waste from swimmers, such as sweat, urine and stool. CDC’s 2007 report on an indoor pool illness outbreak in Nebraska describes this reaction and notes that low pH speeds up formation of the most irritating type of chloramine.
The more waste that enters the water, the more chloramines form. That is why pre-swim showers, bathroom breaks and keeping urine out of the pool make a difference. Read more about what happens when urine mixes with pool chlorine.
Why does an indoor pool smell like chlorine?
The strong “chlorine” smell at an indoor pool comes from chloramines in the air. The 2007 CDC report explains that the most volatile type of chloramine moves from the water into the air most readily and causes the most irritation.
CDC’s 2025 operator guidance says chloramines are heavier than air, so they settle just above the water where swimmers and spectators breathe. Three things make them build up in indoor air:
- Splashing and other activity that disturbs the water’s surface
- Little fresh air moving across the water
- Air handling systems that bring in too little outdoor air and exhaust too little pool air, which is more common in winter when heating costs are high
For homeowners, what causes pool chlorine smell and how to get rid of it covers the same problem in backyard pools and spas.
Are chloramines harmful?
Chloramines irritate the skin, eyes and respiratory tract, including the nose, according to CDC’s 2025 guidance. At high levels in a poorly ventilated indoor pool, they can make many people sick at once.
CDC’s 2007 report describes one example. In December 2006, 24 guests became ill after using an indoor motel pool in Nebraska, with symptoms such as burning eyes, coughing, wheezing and chest tightness, and a 6-year-old boy was admitted to intensive care. The pool’s combined chlorine was 4.2 ppm, far above the 0.5 ppm limit, its pH was 3.95, and the ceiling exhaust fan was off. Investigators did not measure chloramines in the air, but they concluded chloramines were the likely cause.
Research on chloramines and long-term lung health is still developing, especially for elite swimmers and pool staff who spend hours a day at indoor pools. For what the studies show, see why so many elite swimmers have asthma and what the research says about swimming with asthma or allergies. For one swimmer’s experience, read how chloramines affected my lungs as a swimmer.
Do red eyes after swimming come from chlorine or chloramines?
Red, stinging eyes after swimming are often linked to chloramines and to pH that is out of range. CDC lists eye irritation among the effects of chloramines, and CDC’s healthy swimming guidelines note that pH outside the 7.0 to 7.8 range makes chlorine work less well and can irritate skin and eyes. Keeping waste out of the water and keeping pH in range are the two best ways to prevent red eyes.
What combined chlorine level is too high?
Most health departments limit combined chlorine in public pools to 0.4 ppm or less, according to CDC’s 2025 operator guidance. A reading above that limit is a signal to act. A strong chemical smell, red eyes or coughing among swimmers and staff are also warning signs, even before a test confirms it.
How do you get rid of chloramines and chlorine smell at an indoor pool?
CDC’s 2025 guidance recommends these steps for public pool operators:
- Require swimmers and staff to rinse off before entering the water, and post signs in locker rooms.
- Measure free and total chlorine, and calculate combined chlorine by subtracting free from total.
- When combined chlorine is too high, close the pool, make sure ventilation is running, superchlorinate by raising free chlorine to 10 times the combined chlorine level, and then return free chlorine to the normal operating range before reopening.
- Set up air handling to move fresh air across the water’s surface toward exhaust vents, exhaust pool air outdoors and bring in outside air, even when that raises heating costs.
- Consider a supplemental system that breaks down chloramines. CDC names UV and ozone systems, which also kill Crypto.
Hydroxyl-based AOP is another supplemental option. In Clear Comfort’s commercial case studies, facilities have reduced chloramines and other disinfection byproducts by 50% to 90%, depending on the byproduct measured and facility conditions (YMCA case study; UV comparison case study). These are case-specific results, not guarantees. Clear Comfort is supplemental, so pools still keep a chlorine residual.
Facility operators can find more detail in 3 ways to lower combined chlorine in swimming pools.
How can swimmers and home pool owners reduce chloramines?
Swimmers can cut chloramines at the source. CDC’s guidance for swimmers recommends:
- Rinse off for at least 1 minute before getting in.
- Use the toilet before swimming, and take children on hourly bathroom breaks.
- Never urinate or defecate in the water.
- Wear a swim cap.
- Stay out of the water if you have diarrhea.
The 2007 CDC report also advises swimmers to tell pool staff about strong chemical odors or eye and breathing irritation, and to leave the area until it is fixed.
At home, the same habits help, along with keeping pH in range and shocking the pool when needed. A supplemental system lets you run a low-chlorine pool: with hydroxyl-based AOP, typical free chlorine is 0.5 to 1.5 ppm. See how to lower chlorine in your pool for a step-by-step guide.
Frequently asked questions
What is the difference between chlorine and chloramines?
Free chlorine is the chlorine in pool water that is still available to kill germs. Chloramines form when that chlorine reacts with sweat, urine and other waste from swimmers. Chloramines cause most of the pool smell and irritation that people blame on chlorine.
Does a strong chlorine smell mean the pool is clean?
No. A strong “chlorine” smell at a pool usually means chloramines have built up in the water and air. CDC lists chloramine odor as a warning sign for pool operators to act on.
What combined chlorine level is too high?
Most health departments limit combined chlorine in public pools to 0.4 ppm or less, according to CDC. Above that level, CDC recommends closing the pool, ventilating and superchlorinating before reopening.
Does showering before swimming reduce chloramines?
Yes. Rinsing off for at least 1 minute removes sweat and other material that would otherwise react with chlorine. CDC recommends it for all swimmers and suggests operators require it.
How do pool operators remove chloramines?
CDC recommends superchlorinating to 10 times the combined chlorine level, improving fresh air flow across the water and requiring pre-swim rinses. Supplemental systems such as UV, ozone or hydroxyl-based AOP can also break down chloramines alongside chlorine.
See how Clear Comfort’s hydroxyl-based AOP helps pools and spas keep chloramines low with a low chlorine residual.
