A study by the Catholic University of Louvain in Brussels, Belgium found a link between swimming in chlorinated pools and getting asthma and respiratory allergies.

“The impact of these chemicals on the respiratory health of children and adolescents appears to be much more important — at least by a factor of five — than that associated with secondhand smoke,” according to toxicology professor Alfred Bernard.

“There is little doubt that pool chlorine is an important factor implicated in the epidemic of allergic diseases affecting the westernized world.”