Door knobs come in many shapes, finishes, and styles. For the most part, these differences are just a matter of taste, with some variation between one look or another depending on an individual’s preference in design. But when it comes to the material the door knob is made of—whether brass, chrome, plastic or stainless steel—the choice can have serious health implications.
This is because copper and its alloys, particularly brass, have been found to be self-disinfecting. Surfaces that are touched frequently, from shopping carts to the elliptical machine at your gym, are often crawling with bacteria. That goes for door knobs, too, of course. (One study found that Starbucks door handles carried more bacteria than a New York City subway pole.). However, when those door knobs are made of brass or copper, a chemical reaction helps to reduce this germ build up.
It all boils down to what scientists call the “oligodynamic effect,” the term for when metal ions in brass have a toxic effect on living cells and bacteria, even in low concentrations. As one study from the National College of Kathmandu in Nepal found, “the metal ions denature protein of the target cells by binding to reactive groups resulting in their precipitation and inactivation. The high affinity of cellular proteins for the metallic ions results in the death of the cells due to cumulative effects of the ion within the cells.”
So brass effectively sterilizes the bacteria from all those hands turning the knobs.
Of course, manufacturers didn’t necessarily know this when they started using brass to make door knobs. Brass is durable and resistant to corrosion, making it an attractive option from early on in the door-knob-making process, when knobs were first created by brazing two pieces of metal together and then through casting beginning around 1846. While brass remains the most common type of metal used for door knobs, stainless steel and plastic have grown increasingly popular (and cheaper) as a material choice—and that may be bad news for cutting back on the spread of germs.
Professor Bill Keevil, head of the microbiology group at Southampton University, explained to Business Insider that, “On stainless steel surfaces these bacteria can survive for weeks, but on copper surfaces they die within minutes,” drawing on findings he and his team published in the journal Molecular Genetics of Bacteria. “We live in this new world of stainless steel and plastic, but perhaps we should go back to using brass more instead.” And for more amazing facts about the germs living around us, don’t miss these 20 Shocking Facts About Your Hotel Room.
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