I don’t know if it affects growth. i think it helps to protect the hair and to make it more water-proof.
These days when most people wash their hair regularly it doesn’t have time to get oily. The experiment to do (if you want to volunteer) is to stop washing your hair for a month or two and see how it goes.
But I’m not sure how you would do a fair test… you would probably have to use a large group of people who release very different amounts of oil from their scalps and compare how their hair grew.
Hmmmm not sure about that. I used to stand on my head as I heard that helped your hair grow faster (since more blood goes there), but i’m not sure about that either…it doesn’t look like there is much reliable evidence either way.
I couldn’t find a clear answer to this one on the internet, and I am no expert in hair growth (although I have a very fine mane). The web seems full of adverts for oils that can make it groiw or stop it falling out (more like snake oil, I suspect). The only relevant science I could see (it was a very quick look) suggested that both sebum (the oily substance produced by your head) and hair growth are influenced by the same hormone testosterone, but if anything it seems to work the other way round so that hair loss is associated with high levels of sebum. This is all based on a very non-scientific survey of links on Google I am afraid.