Castor oil is an irritant. When you apply it to then scalp , the skin there gets irritated and this increases the blood supply and this increases the rate of hair growth. BUT since it is an irritant, it damages the cuticle thus possibly leading to frizzy and dry hair. Coconut oil acts like a conditioner..according to me it doesn't have any effect on hair growth. It does leave the hair smoother because of the conditioning effect. My usual suggestion to my patients is to apply only coconut oil on the hair that fall below the ears (for women) just 15 min before a bath. It helps softening and reduces dryness of hair tips and split ends. As for hair growth : my suggestion to patients is to IMPROVE Eating habits and sleeping habits . Your hair is the Biggest indicator of your health . Stay healthy by sleeping on time 10 pm, eating a balanced diet on time and exercising 60 min everyday and your hair will automatically get healthier. There is no quick fix solution like oiling of hair to increase thickness. Else in a country like India where everyone uses some kind of oil or the other, there would be no bald people at all. But that's not true is it ?