Ok I've been looking into this too. My hair has been thinning (at least I think so) along my part and my hairline in the front. I use castor oil on my hairline a couple times a week and on my eyebrows and eyelashes every night. I noticed a definite difference on my eyebrows. I also use coconut oil mixed with peppermint essential oil all over my scalp. I do this once or twice a week. (I wash my hair every 2-3 days for reference). Peppermint essential oil is a vasodilator which means your scalp will get more blood flow and your hair will have more nourishment from it. Also, peppermint oil feels nice when you use it :) they say (diluted) tea tree oil does this as well. I've also read that lavendar essential oil as well as rosemary essential oil have similar effects. I have not yet tried them though. Rosemary oil and peppermint oil have studies to back up their effectiveness. There aren't many studies on castor oil but I've heard a lot of people using it for hair growth which is why I am too. Since starting my oiling regimen my hair has has less loss along the hairline and the baby hairs have gotten longer!