I've had long hair for most of my life and being a NEET, I was a greasy fuck.
My hairstyle was split in the middle, and that was the exact spot that I didn't brush for like 5 years.
When I shaved my hair short for the first time, I could see a literal ridge of thickened, hard skin along where my hair used to split.
And all of the hair loss was along that ridge.
Easy way to test if you have thickened scalp due to sebum buildup:
Press down with your mid-finger knuckles on your skull bone somewhere on the side of the head. It's kinda painful, right.
Now do the same to the spot where you have hair loss. If you don't feel as much pain and your knuckle is being cushioned like there's a pillow under your skin, then you have excess sebum.
