Have you ever set a cement block or something as equally flat and heavy on the ground? And then a few weeks later a weed that was sprouted when you put the block there, forces it's way out from underneath the block.
I've been wearing a cap my whole life.
After about forty years of this, the cap won't let the hair grow on top of my head anymore so the hair is being forced out my ears, neck, back, and the inside and outside of my nose.
This hasn't been a carefully monitored, double blind study. Just an observation by me.