Disinfection byproducts (DBPs) are compounds that form when chlorine in pool water reacts with sweat, urine, skin cells, lotions and other organic matter that swimmers bring in. The best known are chloramines, which cause most “chlorine smell,” red eyes and itchy skin; others include trihalomethanes (THMs) and haloacetic acids (HAAs). Pools need chlorine to control germs, so the practical goal is to keep the organic load low and remove DBPs as they form.
What are disinfection byproducts in a swimming pool?
DBPs are the unintended products of disinfection. Chlorine does its job by reacting with germs and organic material, and some of those reactions leave new compounds behind in the water and the air above it. A 2010 study in Environmental Health Perspectives by Susan Richardson and colleagues identified more than 100 DBPs in pool water, many of them nitrogen-containing compounds that likely formed from human inputs such as urine, sweat and skin cells.
The main groups pool owners hear about are:
- Chloramines (combined chlorine): form when chlorine binds to sweat, urine and other body waste. They cause the sharp pool smell and most eye and skin irritation.
- Trihalomethanes (THMs) and haloacetic acids (HAAs): two other DBP groups that labs measure in pool water, as in the YMCA case study below.
Where do DBPs in pool water come from?
Every swimmer adds organic matter: sweat, urine, skin cells, hair products, lotions and dirt. Outdoor pools also collect leaves, pollen and other debris. The CDC explains that when chlorine binds to the body waste swimmers bring into pools, it forms chloramines. CDC also notes that chlorine used up this way leaves less chlorine available to kill germs.
More swimmers means more organic matter for chlorine to react with, so busy pools need the most attention.
Does a strong chlorine smell mean a pool is clean?
No. A strong smell usually points to a DBP problem. The CDC says that if you smell “chlorine” at the place you swim, you are probably smelling chloramines, and that these irritants can become airborne, especially in indoor pools with weaker ventilation.
Why do my eyes turn red after swimming?
Red, stinging eyes after a swim are usually caused by chloramines, which form when chlorine reacts with sweat, urine and dirt. CDC lists red and itchy eyes, skin irritation and rashes as common effects of these irritants. Showering before swimming, bathroom breaks and good water and air management all reduce them.
Are disinfection byproducts harmful to swimmers?
The short-term effects are well documented. The CDC says chloramines irritate the skin, eyes and respiratory tract once they off-gas into the air, creating an unhealthy environment for swimmers, spectators and staff.
Longer-term effects are less certain. In a 2010 study of 49 healthy adults, Manolis Kogevinas and colleagues found that 40 minutes of swimming in an indoor chlorinated pool raised markers of genetic damage in blood and urine. The authors called these preliminary results that need confirming in larger studies, and said the health benefits of swimming can be kept by reducing the chemicals involved. That is the balanced takeaway: swimming is good for health, and lower DBP levels make it better.
Who is most exposed to pool DBPs?
- Pool staff and lifeguards: a 2007 study in the European Respiratory Journal of 624 indoor pool workers found that those with higher chloramine exposure reported upper respiratory symptoms more often.
- Competitive swimmers: long, hard training breathing pool air is linked to higher asthma rates; see why so many elite swimmers have asthma.
- Children: see what parents should know about pool chlorine and kids.
- Indoor pool users in general: byproducts that leave the water build up in the air when ventilation is weak.
Do salt water pools have disinfection byproducts?
Yes. A salt water pool is a chlorine pool. The Indiana Department of Health explains that a salt chlorinator makes chlorine from salt using an electrical charge, and that the chlorine produced from the salt is the disinfectant. That chlorine reacts with sweat and other organic matter the same way, so salt pools form DBPs too.
How can you reduce disinfection byproducts in a pool?
For swimmers:
- Shower for at least 1 minute before swimming: the CDC says a one-minute rinse removes most of the dirt and sweat that help form chloramines.
- Take bathroom breaks: CDC recommends taking kids on bathroom breaks and checking diapers every hour.
- Wear a swim cap and keep lotions and hair products to a minimum before getting in.
For pool owners and operators:
- Keep chlorine and pH in range for your pool and local code, and test often.
- Watch combined chlorine: CDC tells operators to monitor it and treat the water when levels run high.
- Ventilate indoor pools: CDC recommends bringing fresh outdoor air into the swimming area.
- Add supplemental oxidation: Clear Comfort’s hydroxyl-based AOP works alongside a low chlorine residual to break down chloramines and other byproducts.
Clear Comfort is a supplemental system, so pools still keep a low chlorine residual; with hydroxyl-based AOP, typical free chlorine runs 0.5 to 1.5 ppm in residential pools. In Clear Comfort’s commercial case studies, chloramines and other DBPs dropped by 50% to 90%, with results varying by site. In one YMCA pool, total THMs were 84.8% lower after installation, based on samples taken in March and June 2015 and analyzed by the University of Colorado Boulder. Facility operators can find more in how pool disinfection byproducts affect asthma and allergies and 3 ways to lower combined chlorine.
Frequently asked questions
What are DBPs in pool water?
DBPs, or disinfection byproducts, are compounds that form when chlorine reacts with sweat, urine, skin cells and other organic matter in pool water. Common examples are chloramines, trihalomethanes (THMs) and haloacetic acids (HAAs). Researchers have identified more than 100 DBPs in pool water.
How do I get rid of chlorine smell and red eyes from my pool?
The smell and red eyes usually come from chloramines, so the fix is to reduce chloramines. Ask swimmers to shower before swimming, keep chlorine and pH in range, check combined chlorine, and ventilate indoor pools. A supplemental system such as hydroxyl-based AOP can help break down chloramines as they form.
How do I get rid of chloramines and chlorine smell at an indoor pool?
Indoor pools reduce chloramines by limiting what swimmers bring in, removing byproducts from the water and moving them out of the air. CDC guidance for operators includes pre-swim showers, monitoring combined chlorine, treating the water when it runs high and bringing in fresh outdoor air. Supplemental treatment such as hydroxyl-based AOP can help break down chloramines in the water.
Are pool disinfection byproducts dangerous?
Chloramines are known to irritate the eyes, skin and airways, especially in poorly ventilated indoor pools. Some studies have found early signs of longer-term effects, but researchers describe those results as preliminary. Swimming remains healthy, and lowering DBP levels reduces the risks.
Do salt water pools produce DBPs?
Yes. Salt water pools use a generator that makes chlorine from salt, and that chlorine reacts with sweat and other organic matter just as it does in any chlorine pool. Salt pools need the same attention to DBPs as other chlorinated pools.
Does showering before swimming really reduce DBPs?
Yes. The CDC says a one-minute rinse removes most of the dirt and sweat on the body, which means less material for chlorine to react with. Fewer reactions mean fewer chloramines and other byproducts in the water and air.
Want fresher-smelling water at home? See how Clear Comfort works for residential pools.
