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New York - Swimming in chlorinated pools may increase the risk of a child getting asthma and respiratory allergies like hay fever, according to a Belgian study.

Researchers from the Catholic University of Louvain in Brussels, Belgium, found that teenagers who spent more than 100 hours swimming in chlorinated pools were up to six times more at risk of having asthma than other teens.

"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," toxicology professor Alfred Bernard told Reuters Health.

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

In the study, Bernard and his colleagues compared the health of 733 teenagers aged 13 to 18 who swam in chlorinated pools for various amounts of time with that of 114 teenagers who swam mostly in pools sanitized with a mix of copper and silver.

Among "sensitive" adolescents, the odds for hay fever were between three and six times higher for those who swam in chlorinated pools for more than 100 hours, the researchers reported in the journal Pediatrics.

Changes in the airway

The odds of allergic rhinitis were increased two to three times among those who logged more than 1 000 hours in chlorinated pools.

Among children and teens who swam in chlorinated pools for between 100-500 hours, 22 children out of 369, or 6%, had current asthma, compared with only 2 of 144, or 1.8%, of those who had spent less than 100 hours in chlorinated pools.

The proportions with asthma rose with longer exposure, to 14 out of 221, or 6.4%, who had been swimming for 500-1 000 hours, and 17 out of 143, or 11.9%, for those who swam for more than 1 000 hours.

The risk of asthma and allergy was not influenced by swimming in copper-silver sanitised pools and children without allergic tendencies were not at increased risk of developing allergies.

"The only plausible explanation" for these observations, the researchers said, is that the chlorine-based toxic chemicals in the water or hovering in the air at the pool surface caused changes in the airway and promote the development of allergic diseases.

"It is probably not by chance that countries with the highest prevalence of asthma and respiratory allergies are also those where swimming pools are the most popular," said Bernard.

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Swimming in a chlorinated pool may boost the odds that a child susceptible to asthma and allergies will develop these problems, a study released today indicates.

"These new data clearly show that by irritating the airways of swimmers chlorination products in water and air of swimming pools exert a strong additive effect on the development of asthma and respiratory allergies such as hay fever and allergic rhinitis," Dr. Alfred Bernard, a toxicologist at the Catholic University of Louvain in Brussels, Belgium, noted in an email to Reuters Health.

"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 5 - than that associated with secondhand smoke," Bernard noted.

Taken together with his team's prior studies, he added, "There is little doubt that pool chlorine is an important factor implicated in the epidemic of allergic diseases affecting the westernized world."

In the current study, Bernard and colleagues compared the health of 733 adolescents, 13 to 18 years old, who swam in chlorinated outdoor and indoor pools for various amounts of time with that of 114 "control" adolescents who swam mostly in pools sanitized with a concentration of copper and silver.

In children with allergic sensitivities, swimming in chlorinated pools significantly increased the likelihood of asthma and respiratory allergies, the researchers report in the journal Pediatrics.

Among "sensitive" adolescents, the odds for hay fever were between 3.3- and 6.6-fold higher in those who swam in chlorinated pools for greater than 100 hours and the odds of allergic rhinitis were increased 2.2- to 3.5-fold among those who logged more than 1000 hours of chlorinated pool time.

For example, among children and teens who swam in chlorinated pools for 100-500 lifetime hours, 22 children out of 369 (6.0%) had current asthma, compared with those who had spent less than 100 hours (2 of 144, 1.8%). The proportions with asthma rose with longer exposure, to 14 out of 221 (6.4%) who had been swimming for 500-1000 hours, and 17 out of 143 (11.9%) who swam for more than 1000 hours.

The risk of asthma and allergy was not influenced by swimming in copper-silver sanitized pools and children without allergic tendencies were not at increased risk of developing allergies.

"The only plausible explanation" for these observations, the researchers argue, is that the chlorine-based toxic chemicals in the water or hovering in the air at the pool surface cause changes in the airway and promote the development of allergic diseases.

"It is probably not by chance," Bernard told Reuters Health, "that countries with the highest prevalence of asthma and respiratory allergies are also those where swimming pools are the most popular."

The current findings, he and colleagues conclude, "reinforce" the need for further study on the issue and to enforce regulations concerning the levels of these chemicals in water and air of swimming pools.

Do you have a problem with chlorinated pools?

Pool chlorine tied to lung damage

Paris - Competitive swimmers who train at indoor chlorinated swimming pools may have lung changes similar to those seen in people with mild asthma, according to an international study, although there is no evidence those changes lead to actual asthma.

To obtain findings published in the Journal of Allergy and Clinical Immunology, researchers from France and Canada compared lung tissue and breathing tests from 23 elite Canadian swimmers, whose average age was 21, to 10 mild asthmatics and 10 healthy people without allergies of the same age.

The team, led by Valerie Bougault at the Lille 2 University of Health and Law in France, found that 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.

"Intense, long-term swimming training in indoor chlorinated swimming pools is associated with airway changes similar to those seen in mild asthma," wrote Bougault.

Swimmers and asthmatics also showed evidence of scar tissue in the lungs, while healthy non-swimmers did not.

Common allergens

"This study is the first to show direct evidence of airway damage associated with swimming in chlorinated pools," said Alfred Bernard, a toxicologist at the Catholic University of Louvain in Brussels, Belgium. Bernard was not involved in the study.

Tissue samples and tests were taken during the off-season when the swimmers were not competing.

Lung tissue inflammation was not associated with actual asthma symptoms, such as coughing and wheezing, or with difficulty breathing during a medical test used to determine lung function.

While acting as a disinfectant, chlorine reacts with a wide range of chemicals from human sweat, urine and hair, for example, to form chlorine by-products, some of which are hazardous to human health. These by-products are very volatile and can escape into the air above the water.

Competitive swimmers are known to inhale large amounts of these chlorine by-products while doing strenuous exercise in the pool, and exposure to the chlorine compounds in indoor pools may make swimmers more sensitive to other allergens such as pet dander, pollen and dust, wrote Bernard.

Roughly 50% to 65% of competitive swimmers are sensitised to common allergens, compared with 29% to 36% of people in the general population, he added.

But it was not clear if exposure to the chemicals caused the lung tissue damage. A study of elite cross-country skiers showed that the stress placed on lungs during high-level endurance sport training itself might be enough to induce airway changes.

"There's currently no evidence to suggest that these changes will lead to asthma down the line," said Sally Wenzel, a pulmonologist at the University of Pittsburgh, adding that it was likely the benefits of exercise outweigh potential risks.