An old wife's tale (or not?) is to rub castor oil on your scalp. It is supposed to make hair grow in thicker and faster. I don't know about all that. I do know for a fact that this helps with a dry scalp. I had the worse dry scalp ever - flaking, patchiness and used a hair lotion w/castor oil (BB Moisturizing Lotion). Just a little at night massaged into my scalp. Totally eliminated the problem.
Something is helping my hair grow faster, but I think it is the supplements I take for PCOS - flaxseed oil and cinnamon, helping more than the castor oil. I've been using the castor oil for a long time, and the faster growth is a new phenomenon.