How Hair Strands Make Razor Blades Chip And Crack Hair is soft compared with steel, but shaving can dull a razor surprisingly quickly. A new study examines exactly how a strand of hair can chip and crack a sharp blade.

Cutting-Edge Research Shows How Hair Dulls Razor Blades

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STACEY VANEK SMITH, HOST:

Now for some truly cutting-edge research on razors. Disposable razor blades can get dull very quickly. Turns out something as soft as hair takes a toll on stainless steel, and researchers got an up-close look at how. NPR's Nell Greenfieldboyce reports.

NELL GREENFIELDBOYCE, BYLINE: Gianluca Roscioli is a graduate student at MIT. Not too long ago, he bought some everyday drugstore razors and used a powerful scanning electron microscope to get images of each blades' edge. Then he used the razors to repeatedly shave his own face.

GIANLUCA ROSCIOLI: The way I did it was, first, imaging the entire blade. Then, every three days old, the beard, I shave it and image the blade. And after three days, shave again, image the blade, and so on.

GREENFIELDBOYCE: He and his colleagues expected to see a gradual rounding of the blade's tip. That did happen - very slowly. What happened immediately was something completely different.

ROSCIOLI: The more I shaved, the more chips started appearing on the blade.

GREENFIELDBOYCE: These chips were teeny-tiny.

ROSCIOLI: The size of the chips are about one-tenth of the diameter of human hair. So they are not visible by human eye.

GREENFIELDBOYCE: It wasn't clear how soft hairs could trigger this chipping, so he set up an experiment that let him use the microscope to watch a razor blade as it cut through strands of hair. The results are in the journal Science. Cem Tasan is head of this MIT lab. He says the angle at which the blade meets the hair turns out to be really important. But knowing that won't help you make your razor last longer.

CEM TASAN: If you're shaving, obviously your hair is looking in different directions. And as the blade cuts through them, it's difficult to control in each case of what this angle is.

GREENFIELDBOYCE: Tasan says another thing that mattered was where the hair was in relation to little micro-cracks found in all blades, even unused ones.

TASAN: If these micro-cracks are positioned just at the edge of the hair that's being cut, these cracks propagated more easily.

GREENFIELDBOYCE: Again, that's impossible to control in the real world, but Tasan says their research does point to ways of reducing this chipping, like coming up with blades that have a more uniform internal structure. Suveen Mathaudhu is a material scientist at the University of California, Riverside, who wasn't part of the research team.

SUVEEN MATHAUDHU: I've been shaving since I was 13, and it's a pain.

GREENFIELDBOYCE: He thought corrosion from water would play more of a role in dulling a razor.

MATHAUDHU: But it does make sense that at the very edge of a thin blade, if it's hard, that the conditions of bending of the hair and the conditions of the angle of interaction of the blade could cause chipping.

GREENFIELDBOYCE: He says after thousands of years of making cutting tools, people are still learning how to produce the perfect blade for a job. Nell Greenfieldboyce, NPR News.

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