I've noticed whenever I shave my beard it sometimes takes a couple of pressed strokes with my razor to get it done with no damage to the skin. So that got me thinking what about with the hair growing on top of my head? Would that protect me from knife slashes? Then about chest hair is that there to protect me from knife strikes and can it to a certain degree along with hard tough muscles? Darwin postulated that lions grew out their manes to protect themselves from other predators and lions from biting their neck. Could human hair also provide this protection to a certain degree? Like growing hair down to your neck can protect the neck and head. Of course it's not like I would just stand there and let them slash me but I could avoid a deeper cut with longer hair and pulling away from the attack.
I'm afraid you'll get no additional protection. Consider that a decent blade will cut through thick rope.
Safety razors (the clue is in the name) are designed to cut your hair, not the skin. Knives are the opposite.
Bear in mind you drag the razor going across the length of the blade rather than along it. Using a knife usually involves slashes and cuts using edge alignment and/or stabs using the point. Totally different propositions. Although I'd be willing to bet a full head of luscious locks as sported by Jason Momoa might offer slightly more protection than going full captain Picard it'll be so slight as to be negligible in actual reality.
