Swimming is undoubtedly an excellent exercise for all ages especially for obese to reduce weight and patients of osteoarthritis to keep joints free. The hygiene of indoor pool water is an important factor especially when pools used by many.

It is achieved commonly by adding chlorine and bromine. Other methods like Advanced oxidation process (AOP) do exist, but not adopted by many. The water is also recycled and evacuated periodically.

Now, at least results from three independent researches available, which point to possible DNA damage from the by- products of disinfectants (DBP) like chlorine and bromine.

Chlorine in water produces hypochlorous acid and sodium hypochlorite which act against pathogens in water. They also point out that these chemicals react with urine, sweat, cells from body and cosmetics to produce harmful substances; which may cause DNA damage. That may increase the risk of cancer.

These DBPs enter body from inadvertent drinking of pool water, water absorption through skin and inhalation of exhaled breath of swimmers

They estimated the biomarkers from swimmers who took 40 minutes swimming and found fivefold rise in two mutagenic markers from exhaled breath. Those are micronuclei in blood lymphocytes, which have been associated with cancer risk in healthy subjects; and urine mutagenicity, which is a biomarker of exposure to genotoxic agents.

Another group of researchers found increase in at least one genotoxic substance, serum CC16 in volunteers who inhale the exhaled breath of swimmers rich in DBPs (trihalomethanes). This indicates increases lungs tissue permeability, which may also be exercise induced.

Further the researchersidentified 100 DBPs in swimming pool water. Some are not chemically identified. They say that though these are identical to chlorinated drinking water, are more toxic.

More detailed study in this field is required. Though swimming has not to be discouraged; at the same time swimming pool safety rules must be followed strictly e.g. taking preliminary bath, not urinating in pool water, not swallowing pool water and wearing dress as specified. Further chlorination method of disinfection may be dispensed with in favor of AOP and other safe methods of disinfection.