When I yank out a stray hair, sometimes so goo comes out with it. Are those fat cells? Wet skin cells? Or is that just puss? Or something else? I think it is scraped out with the bulb if the bulb has a large diameter when it is plucked.
Could that be sebum mixed with some dead cells? Whatever it is, it could only have come from the scalp - not from outer space .
My (and somebody's else's) theory is: when men decided to wear their hair short and not brush them as often as women do - about 30 times more often - sebum, oils or whatever that was being secreted by the scalp, became an issue for men.
I don't think that goo will be there if we follow women's natural instinct to brush their hair often before going to bed.
Since most of us wear short hair, the only way to mimic brushing is massaging and wiping it with a towel which is part of my regimen.