European scientists believe that swimming in indoor, chlorinated pools may further aggravate or even create people's asthma. "We unexpectedly found that the main factor affecting the lung (cells) of children was the regular attendance of an indoor chlorinated pool. Pursuing our investigations, we found that regular chlorinated pool attendance was strongly associated with an increased risk of developing asthma," say the authors of Occupational and Environmental Medicine, May issue.

This could explain the global surge in childhood asthma. Public pools in the United States have an average chlorine level of 3 ppm (parts per million). 30 ppm of chlorine causes immediate chest pain and vomiting, and 430 ppm is fatal within thirty minutes.

A study behind this theory tested 226 healthy, primary school children. Their blood was tested before and after swimming to find the levels of chlorine byproduct trichloramine. This is a harmful gas created created by the interaction of chlorine...