The video below by Chescalocs shows off the results of using Jamaican black castor oil for over a year on a thinning hairline. As mentioned in the video, one of the causes to a thinning hairline is too much stress on the hair follicles due to tight hair twisting and braiding styles.
The best way to achieve maximum hair growth is to apply black castor oil on the hairline or other thinning areas on the scalp every day. Also for the best results when twisting or doing braids is to do it on wet or damp hair, when doing it on dry hair breakage can occur which you want to completely avoid. For more information on this subject, watch the video below.