A study shows that competitive swimmers using indoor pools to train, may develop changes in the lungs, similar to those seen in people with mild asthma.
Chlorine, used as a disinfectant in pools, reacts with sweat and hair to release harmful chlorine by-products into the air above the water.
The frequent and prolonged exposure to these chemicals experienced by swimmers during training may also cause them to develop other allergies, such as to pollen, dust and pets.
Researchers in Canada and France compared lung tissue and breathing tests from 23 competitive swimmers with 10 people with mild asthma and 10 people without allergies or asthma.
The results showed similar amounts of immune cells in the lungs of the swimmers and people with mild asthma, which was up to six times greater than found in the lungs of people without allergies. The swimmers and people with asthma also had similar amounts of scar tissue in their lungs. However the swimmers did not have any other asthma symptoms, such as wheezing, coughing or difficulty breathing.
There is currently no evidence to show that competitive swimmers will later develop asthma. There is also no evidence to show that more moderate use of pools causes lung damage.