To fight the spread of germs, doctors should ditch the handshake and greet their patients with a fist bump instead, a new study says.

Through a series of tests, researchers at the Institute of Biological, Environmental and Rural Sciences at Aberystwyth University in Wales documented that fist bumps are 20 times more hygienic than handshakes. They are also 10 times cleaner than high-fives, according to results published online Monday in the American Journal of Infection Control.

Volunteers donned sterile gloves and dunked their hands into a soup of de-fanged Escherichia coli bacteria. Then they shook hands, high-fived or fist-bumped with one another.

The handshakes transferred an average of 124 million colony-forming units of E. coli. That was almost twice as high as for high-fives and about 20 times more than with fist bumps.

In part, this was due to the large contact area of handshakes. The greater the contact area, the more bacteria moved from hand to hand, but that wasn’t the whole story, the researchers reported.

For instance, the duration of the greeting matters. Handshakes last longer – 3 seconds – than high-fives or fist bumps. When fist bumps were prolonged to 3 seconds, more E. coli spread from hand to hand.

There’s also the pressure between hands during a greeting. An instrument called a dynamometer measured the grip strength of various handshakes and found that those of “moderate strength” transferred fewer bacteria than “strong” handshakes.