If you enjoy a swim at your local swimming pool, be careful how it's being cleaned - it could be increasing your chances of cancer and asthma. Indoor pools that are disinfected with chlorine damage your DNA, and this could lead to cancer and respiratory diseases such as asthma, researchers have discovered this week. Either get the attendants to use less chlorine or find a pool that is cleaned by other methods, such as bromine, they recommend. In the study, the research team found that 49 healthy swimmers were showing genotoxic effects - DNA damage that can lead to cancer - after just 40 minutes swimming in an indoor pool. The real culprit is DBPs - the by-products of chlorine when it is mixed with organic matter such as sweat and skin cells. The researchers discovered more than a hundred DBPs in the pools cleaned with chlorine. (Source: Environmental Health Perspectives, 2010; doi: 10.1289/ehp.1001959).