A study from US researchers claim that using unheated water to wash your hands is as effective at killing bacteria as using hot water.

The small study of 20 people found using water at 15oC left hands as clean as water heated to 38oC.

The study was carried out by researchers at the Rutgers University-New Brunswick in New Jersey, and the results were published in the Journal of Food Protection.

The study examined the effect of various factors, such as soap volume, water temperature, lather time, and the hand washing efficacy of the soap as formulated on the product.

They asked 20 people consisting of 10 men and 10 women to wash their hands 20 times each with water that was 15oC, 26oC or 38oC.

Volunteers were also asked to experiment with varying amounts of soap – ranging from 0.5mm to 2mm.

Before they started the tests, their hands were covered in nonpathogenic strain of Escherichia coli ATCC 11229.

Researchers say there was no difference in the amount of bacteria removed as the temperature of the water or the amount of soap changed.

Prof Donald Schaffner said: “People need to feel comfortable when they are washing their hands but as far as effectiveness [goes], this study shows us that the temperature of the water used did not matter.”

However, the researchers accept their study is small and say more extensive work is needed to determine the best ways to remove harmful bacteria.

In the UK, NHS say people can use cold or hot water to wash their hands. They say hands should be washed for at least 20 seconds and stress the importance of using enough soap to cover the whole surface of the hands.

Their guidance focuses on rubbing hands together in various ways to make sure each surface of each hand is clean.

The NHS’s advice on washing your hands is as follows:

• Washing your hands properly should take about as long as singing Happy Birthday twice (about 20 seconds)
• Wet hands and apply enough soap to cover the whole surface of the hand
• Rub palms together with fingers interlaced
• Rub each palm over the back of the other hand with interlaced fingers
• Rub between fingers on each hand
• Rub backs of fingers (interlocked)
• Rub around each thumb
• Rub both palms with finger tips and then rinse with warm or cold water
• Dry your hands well, ideally with a disposable towel
• Use a disposable towel to turn off the tap