The chemical used to clean indoor pools, called chlorine, is not very good for your lungs, a new study says.
Chlorine can damage the cells in your deep lungs, which could be linked to asthma.
More research
Kids who swim a lot were found to have lungs as bad as some heavy smokers, the researchers found.
How 'tight' children's chests are, and how bad their asthma is, are both linked to how much time they spend in pools.
The number of children getting asthma has shot up in recent years, with all sorts of things like pollution being blamed.
Swimming is actually recommended for people with asthma because the hot air and exercise can help their condition.
They want more studies to be done to see just how bad the effect of chlorine is on children's lungs.
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