I would think that sharp razors, being sharper, would cut better.
I always assumed that it’s because the duller blade hangs up on the hairs instead of slicing neatly through them, and is thus deflected downwards onto your skin, which it then cuts.
That is what I think as well. A really shape blade will slide across the surface of your face mowing everything it its path smoothly. Dull blades grab and chatter as they get hung up on hair.
You also tend to press harder on a dull blade.
Sharp razors *do * cut better, if cutting skin is what you are trying to do. But somehow I don’t think that’s what you’re asking.
When shaving, a sharp razor won’t cut smooth skin if it moves in a direction strictly perpendicular to the edge of the blade. People who use straight razors know all about this. But a dull razor does not develop a smooth, dull edge. It develops a ragged edge, and so I think the rough edges can cause problems. You would probably shred your face if you tried to shave with one of those cheap never-needs-sharpening knives, for example.
I see it in 1970s razor commercial graphics:
“The first blade grabs the hair and uses it to pull the skin up - the second blade spills blood.”
Update to present:
…the third blade neatly slices chunks off your face
…the fourth blade gently removes your ear
…the fifth blade slides effortlessly across your throat with a gentle whisper
Don’t forget the moisturizing strip designed to irritate the shit out of any nicks you make!
Ever heard Bill Cosby do Little Tiny Hairs?
“The razor people go through a lot of trouble to put numbers on those things so no matter what number you turn to you still cut yourself to pieces”
You see, back in the dark ages, instead of multiple blades they had this little dial with numbers.
ETA - http://youtube.com/watch?v=cLVum97SozE starting about 5:30