Q How hot does water have to be to kill germs in domestic laundry?
A "It is hard to find standard guidelines on water temperatures for domestic laundry," said Dr Alexandra Sowa, an internist at New York-Presbyterian Hospital/ Weill Cornell Medical Centre.
Even the United States' Centres for Disease Control and Prevention (CDC) provides only a recommendation to follow the label.
The CDC says that hot water is not necessary for all household laundry and to "wash and dry clothing at the warmest temperature listed on the clothing label".
But some studies suggest that water does not have to be as hot as often thought to get clothes acceptably clean, said Dr Sowa.
One study, done in Britain and published 12 years ago, showed that washing the very dirty clothes of hospital staff at about 37 deg C in a home machine was just as effective at killing one type of bacteria (Staphylococcus aureus) as washing it at a much higher temperature.
However, the study also found that washing the clothes resulted in contamination with new environmental bacteria, very likely from the washing machine itself.
Said Dr Sowa: "To rid the clothes of any pathogens picked up in the wash cycle, the clothes just had to be tumble-dried for 30 minutes or ironed.
"The heat from a low dry cycle or an iron was sufficient to get the clothes free of the studied bacteria."
Dr Sowa recommended that washing machines be periodically cleansed of their considerable amount of bacteria by running them for a regular cycle with bleach and water but without clothing.
She also said that she would err on the side of caution when it came to washing certain items, like dish towels, the clothes of family members with infections, and hospital scrubs, by using water heated to 60 deg C.