Research indicates that exposure to chlorinated swimming pools, particularly indoor pools, may irritate the respiratory system and can aggravate asthma in some people. Experts caution that swimmers should not overlook this potential factor while exercising.

Chlorine is necessary to disinfect swimming-pool water and prevent the spread of disease-causing microorganisms. However, when chlorine reacts with sweat, urine, dirt, and other substances brought into the water by swimmers, it can form chemical irritants called chloramines. These compounds can accumulate in the air above indoor pools and may cause respiratory symptoms such as coughing and wheezing, particularly in people with asthma.

Researchers have paid particular attention to this issue because swimming is often recommended as a form of exercise for people with asthma. The benefits of swimming should therefore be considered together with the quality of the pool water and surrounding air. Proper pool maintenance, adequate ventilation, and good swimmer hygiene can help reduce the formation and accumulation of chloramines.

A strong chemical odor around a swimming pool does not necessarily mean that the pool contains too much chlorine. The familiar “chlorine smell” is often caused by chloramines rather than free chlorine itself. If swimmers notice a strong chemical odor or experience coughing, wheezing, eye irritation, or other respiratory symptoms, they should notify the pool operator.

In some swimming facilities, odors may also come from other areas of the facility, so swimmers should consider the entire swimming environment rather than assuming that a strong smell automatically indicates excessive chlorine in the pool water.

By Michael Chiu, MWS, CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026