Children who swim regularly in chlorinated pools are five times as likely to develop asthma, research has found.
Swimming is recommended as a good form of exercise for asthmatics because the warm humid air is less likely to trigger attacks than other physical activities.
However, recent evidence explained in the European Respiratory Journal suggests that the chlorine used to keep pools clean, may be triggering asthma development.
Belgian researchers carried out lung function tests on 847 secondary school pupils with an average age of 15 years. The parents of these school pupils completed questionnaires about their children's exposure to other known asthma triggers such as pets, tobacco smoke and pollution.
The researchers also worked out the total amount of time children had spent in outdoor pools during their life.
Children who had swum for the equivalent of one hour a week for ten years, more than 500 hours in total, were five times more likely to have the wheezing condition than children who never swam in outdoor pools.
The research team also found that children having regularly attended an outdoor pool before the age of seven were more likely to be allergic to cat or dust mite than those who had never attended an outdoor pool so young.
The researchers concluded that children who regularly attend outdoor pools are likely to have an increased risk of developing asthma.