Scientists from MIT have discovered why razor blades become blunt after repeated use. They did research into why razor blades lose their sharpness. Razor blades are 50 times harder than the hairs they cut. Even though human hair is 50 times softer than the metal of a razor blade, the hair damages the edge of the blade. Razor blades are made from stainless steel. They are usually coated with tougher materials like hardened carbon. The MIT scientists said that each time a blade cuts a hair, the hair causes tiny amounts of damage. A blade usually cuts thousands of hairs in one shaving session. This means the life of a razor blade is limited and will need to be replaced regularly.

The researchers used powerful microscopes to find out how hair damages a razor blade. They got a close-up view of what happens during a shave when the blade cuts a hair. The blade gets damaged in a variety of ways. One way is that a single hair creates a tiny chip on the edge of a blade. This chip becomes bigger as it cuts more hair. After more shaving, the blade loses its ability to cut cleanly and becomes blunt. A researcher said: "We are metallurgists and want to…make better metals. In this case, it was intriguing that if you cut something very soft, like human hair, with something very hard, like steel, the hard material would fail." He said his team is "aiming to solve an important engineering problem".