Sweat can reduce anti-bacterial properties of brass objects

Human sweat can reduce the effectiveness of bacteria-fighting brass objects in hospitals and schools after just an hour of coming into contact with them, according to a new study.
University of Leicester researchers discovered that sweat can cause corrosion of protective qualities of door knobs and taps within an hour of contact.
Copper found in everyday brass items such as door handles and water taps has an antimicrobial effect on bacteria and is widely used to prevent the spread of disease.
Dr John Bond from the University of Leicester's Department of Chemistry found that peoples' sweat can, within an hour of contact with the brass, produce sufficient corrosion to adversely affect its use to kill a range of microorganisms, such as those which might be encountered in a hospital and which can be easily transferred by touch or by a lack of hand hygiene.

"The antimicrobial effect of copper has been known for hundreds of years. 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," Bond said.
"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.

"We have shown that it is possible for sweat to produce an oxide layer on the metal within an hour of contact," Bond said.

"While it is well known that sweat corrodes brass, this is the first study to quantitatively analyse 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," he said.
"My short term advice is to keep the brass in public environments free from corrosion through regular and thorough cleaning. In the longer term, using copper alloys with corrosion inhibitors included in the alloy would be a good choice," Bond said.
"While more research is needed in the study of sweat and brass corrosion, anywhere that needs to prevent the spread of bacteria, such as public buildings, schools and hospitals should be looking at using copper alloy on everyday items to help in avoiding the spread of disease," he said.

The study was published in the journal Applied Surface Science.