If you want to improve both hair thickness and hair growth, rosemary oil is a great choice thanks to its ability to improve cellular generation.

According to one studyTrusted Source, rosemary oil performed as well as minoxidil, a common hair growth treatment, but with less scalp itching as a side effect.

Mix several drops of rosemary oil with olive or coconut oil, and apply it to your scalp. Leave it in for at least 10 minutes before washing it out with shampoo. Do this twice per week for best results.