Your washing machine may not actually rid clothes of harmful bacteria

Cleaning your clothes in a washing machine on even a hot water setting of 60°C (140°F) can fail to remove potentially harmful bacteria – a finding that could also be contributing to the rise of antibiotic resistance.

Research has shown that contaminated fabrics can remain a source of infections for weeks, but also that washing at 60°C with a detergent can rid your clothes of bacteria, as well as removing those stubborn stains.

NHS England, for example, recommends that its healthcare workers wash their uniforms for 10 minutes at 60°C to remove almost all microorganisms, says Katie Laird at De Montfort University in Leicester, UK. “But my issue has always been that you don’t know what the machine is doing.”

So, Laird and her colleagues tested six models of home washing machine to see how well they cleaned fabric samples contaminated with Enterococcus faecium bacteria, which can cause a variety of conditions, including urinary tract infections.

Testing both rapid and standard 60°C cycles, the team found that half of the machines didn’t disinfect the clothing – cut the bacteria numbers by at least 90 per cent – during the former, and one-third still failed during a standard cycle.

“This is because a large proportion of the machines weren’t holding or even reaching the temperatures you think they are, particularly on shorter cycles,” says Laird. “We had one machine that was just functioning at 20°C [68°F] and the person didn’t know.”

Laird and her colleagues also found evidence that microorganisms inside washing machines are developing resistance to detergents, after looking at bacteria before and after a series of washes. DNA sampling revealed that the microbes started to develop genes to help them survive.

The results suggest that using home washing machines to clean healthcare uniforms could be contributing to the spread of hospital-acquired infections and antibiotic resistance, says Laird.

To minimise the number of bacteria and viruses in a home washing machine, Laird suggests people should regularly use washing-machine disinfectants, run a 90°C (194°F) cycle to clean the machine and use a descaler to prevent the build-up of limescale, which can stop the heating element working.