A study of more than 190,000 children across Europe has found that children from areas with a high density of indoor pools were more likely to suffer breathing problems.

Alfred Bernard, who led the study, believes that the breathing problems are caused by nitrogen trichloride, a gassy irritant that is released when chlorinated water comes into contact with urine or sweat. He said that poor ventilation of pools and children spending longer in the water, because of popular features such as slides, exacerbated the problem.

Writing in the journal Occupational and Environmental Medicine, Professor Bernard, who is Professor of Public Health at the Catholic University of Louvain, Brussels, said: “This increasing attendance of swimming pools by children has in turn led to substantial changes in the swimming pool environment, such as higher water temperatures, increased bathing loads . . . All these changes have contributed to raising the levels of chlorination by-products in pool air.”

The researchers asked 13 and 14-year-olds from 21 countries to give details of breathing problems, hay fever and eczema and set the information against the ratio of public swimming pools to population. In Western Europe there was on average one pool per 50,000 people, and in Eastern Europe one per 300,000 people. They found that the asthma rate rose 2.7 per cent and the wheezing rate 3.4 per cent for every additional indoor pool. The asthma and wheezing rate was between 10 per cent and 30 per cent in Western countries and less than 5 per cent in Eastern European ones. Britain had one of the highest rates which may be because it has more pools in schools. Professor Bernard said that taking babies to swimming classes before the age of 2 years could be harmful if there was a history of asthma in the family.

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