of dead skin cells
, skin oils
and probably just plain 'ol dirt
that forms on your scalp
if you don't wash
it regularly. Can also happen in you don't shampoo your hair
Ever since I read the don't shampoo your hair writeup, I've been living in disgusted fear of cradle cap. Mind you, my hair is now less than an inch long all around, and I shampoo daily, being extra careful to scrub the scalp diligently. In fact, when I got my hair cut, I could feel the sebum from my scalp washing out the first time I washed it after that, because my hair was longer (3-4 inches) and I couldn't get at the scalp as well as I would have like. It wasn't a full grown cradle cap, but still, it grossed me out.
Now, to each their own, and I know people say with dreadlocks who probably have cradle cap as well, but I could never be one of them. Eeew. This is one aspect of personal hygiene that I'm a firm believer in modern technology and social practices.