Copper-containing metals like brass have antibacterial properties—a selling point for brass doorknobs, sink handles, and other fixtures in hospitals and schools. This is due to the oligodynamic effect (Greek: oligos = few, Greek: dynamis = force). It was discovered in 1893 by the Swiss Karl Wilhelm von Nägeli as a toxic effect of metal ions on viruses and living cells e.g. algae, moulds, spores, fungi, prokaryotic and eukaryotic microorganisms, even in relatively low concentrations.  This antimicrobial effect is shown by ions of mercury, silver, copper, iron, lead, zinc, bismuth, gold, aluminium, and other metals.

But now, British scientists have found that handling those fixtures can actually disable their germ-killing powers. According to University of Leicester forensic scientist John Bond, human sweat forms a corrosive layer on the metal surface. That blocks an exchange of charged particles that would otherwise kill harmful bacteria. And the fixtures that are handled the most would be the most affected.