Some research suggests that infant swimming in chlorinated pools may increase the risk of lower respiratory tract infections or asthma, but there isn't enough information conclusively linking infant swimming and asthma to warrant keeping healthy babies out of indoor pools.
Some researchers theorize that chlorine — a common disinfectant used to keep pools clean — binds with swimmers' sweat and urine to create byproducts in the water and air that may harm an infant's lungs and put him or her at risk of developing asthma. Indoor pools have higher concentrations of these byproducts than do outdoor pools. Babies are thought to be at particular risk because their lungs are still developing and they tend to swallow irritant-laden water while swimming.
Studies examining the relationship between infant swimming and asthma, however, have produced conflicting results. For example, one 2008 study found that infants who swam at age 6 months had a greater risk of having an episode of chest congestion or wheezing in the chest up to age 18 months — if their mothers had a history of allergies. But another study published the same year found that infants who didn't swim before age 1 had a greater risk of being diagnosed with asthma at age 6. Similarly, a 2011 study designed to explore cause and effect found that swimming didn't increase the risk of asthma or allergy symptoms.
If your baby participates in infant swimming in indoor pools and you're concerned about asthma, opt for a well-ventilated facility. Ideally, staff members will open doors and windows in the pool area and use fans to boost airflow over the surface of the pool when it's crowded. Also, be sure to rinse yourself and your baby in the shower before entering the pool to reduce the formation of irritants in the water.