Why do stainless steel razor blades get dull when cutting (soft) human hair?

That requires a two-part answer.

1) The blade is usually kept so thin that even hair can take some of it's edge off.

2) If razorblades were made to last people wouldn't buy so many hurting company profits. This is also why toothbrushes don't last long at all, manufacturers realize it's more profitable to sell lots of cheap brushes as opposed to a few good ones, the same goes for alot of products these days.

Regards,

Armus

Why do stainless steel razor blades get dull when cutting (soft) human hair?

its because the edge is so thin. human hair is still slightly abrasive.

Why do stainless steel razor blades get dull when cutting (soft) human hair?

Also keep in mind the shaving cream or lotion that you use. Oil based products will dull your blade much faster.