Credit: iFixit
iFixit provides “teardowns” of devices, which involve disassembling them and inspecting the components.
During their teardown of a black iPhone 5, they “found that the side is pretty tough, but the chamfered edge can be susceptible to scuffing, making for a shiny streak on the side.” This matches up with reports some users have had about the durability of the finish at the edge of the phone.
iFixit also makes the following recommendation: “be careful, or get a case.” We agree, but recommend you do both if you’d like to keep your iPhone looking new.
The video below has also been added, which demonstrates how the iPhone 5 is more prone to scratches than the iPhone 4S.