Human Sweat May Cause Bacteria to Thrive on Brass Surfaces

It turns out that human sweat may dirtier than you thought. Scientists have found that sweaty hands can reduce the effectiveness of bacteria-fighting brass objects in hospitals and schools after just an hour of coming into contact with them.

Copper found in everyday brass items, such as door handles and water taps, has an antimicrobial effect on bacteria. In fact, it's often used to help prevent the spread of disease. Yet it turns out that human sweat can, within an hour of contact with brass, produce sufficient corrosion to adversely affect copper's ability to kill a range of microorganisms.

"The antimicrobial effect of copper has been known for hundreds of years," said John Bond, one of the researchers, in a news release. "It is thought to occur as a result of a charge exchange between copper and bacteria, which leads to a degradation of the bacteria DNA. We have discovered that the salt in sweat corrodes the metal, forming an oxide layer on its surface, which is the process of corrosion-and this corrosive layer is known to inhibit the effect of the copper."

In this case, the researchers showed that it's possible for sweat to create an oxide layer on the metal within an hour of contact. This could have implications for locations such as hospitals, which rely on clean surfaces.

"While it is well known that sweat corrodes brass, this is the first study to quantitatively analyze the temporal corrosion of copper alloys such as brass in the first few hours after contact between fingerprint sweat concentrations of salt and the metal," said Bond in a news release. "Opportunities to improve hospital hygiene are being investigated by the University of Leicester from seemingly un-connected areas of research. This research is a different application of the study of fingerprint sweat corrosion of brass, applied to hygiene rather than to crime investigation."

The findings are published in the journal Applied Surface Science.