A new study shows competitive swimmers training at indoor chlorinated pools may have lungs similar to people with mild asthma.

Researchers, led by Valerie Bougault at the Lille 2 University of Health and Law in France, compared data from more than 20 elite swimmers in Canada with 10 healthy people, and 10 mild asthmatics.

“Tissue samples from swimmers’ lungs had nearly six times as many immune cells associated with asthma and allergies as the lung tissue of healthy subjects, a similar amount to what was found in the group with mild asthma,” according to a report published by Reuters.

However, there is no evidence that changes in the swimmers’ lungs lead to actual asthma. Changes may be the result of inhaling disinfection byproducts, or some other factor.

The full study appears in the Journal of Allergy and Clinical Immunology (February 2012). It is one of several recent studies linking DPBs to respiratory issues.