Chlorine is effective at killing pathogens in swimming pools, but it also irritates the skin, eyes and upper respiratory tract of swimmers, according to a study in the journal Pediatrics. Recent research has found swimming in outdoor or indoor chlorinated pools can increase asthma risks. The study found that children who swim in chlorinated pools have a higher risk of asthma, as well as other allergic diseases such as hay fever and allergic rhinitis.

Researchers in Belgium compared the health of adolescents who swim in chlorinated pools to adolescents who swim in pools sanitized with a concentration of copper and silver. In children with allergic sensitivities (atopy), exposure to chlorinated pools significantly increased the prevalence of asthma and respiratory allergies.

Study authors suggest the chlorine-based oxidants in the water or just above the water cause changes in the airway and promote the development of allergic diseases. The findings reinforce the need for further research and to enforce regulations on the level of these chemicals in the water and air of swimming pools.