Research by scientists from Belgium suggests that nitrogen trichloride,
a powerful irritant and byproduct of the chlorine used to disinfect swimming
pools, could be linked to the rising incidence of childhood asthma (Occup Environ Med. 2003;60:385-394).
The researchers measured levels of lung-specific proteins in the blood
of primary school children who had swum regularly at indoor pools since early
childhood. The researchers found a consistent and significant association
between regular attendance at indoor swimming pools with the lung-specific
proteins, which are markers of lung permeability and epithelial damage.
Stephenson J. Asthma and Swimming Pools. JAMA. 2003;290(2):184. doi:10.1001/jama.290.2.184-a