How to use rosemary for best hair results? When not to use it?

The aromatic herb of rosemary is often termed 'nature's serum,' for its potential to give hair growth a power-packed boost. For issues ranging from thinning, dry scalp, dandruff and premature greying to split ends and oily scalp, rosemary knows how to help your hair. And that, too, you need not give it extremely complex treatments to get a good result. According to the dermatologists of the Cleveland Clinic, all you need to exercise is some precautions and ensure the right dosage to get the best results from rosemary for hair growth. And here's what you should know:
1) While applying the oil, focus on your scalp, not the hair, as it will not affect the hair. 
2) While using rosemary oil, avoid oils with fragrance additives known as carrier oils. While many suggest the usage of carrier oils and diluting for good results, Dr Shilpi Khetarpal of Cleveland Clinic observes that only 100% rosemary oil will give you the best benefit. Also, do a patch test on a small area of your scalp first to see how the oil reacts before applying it all over your scalp.

3) All you need to apply is just about a teaspoon of oil for the whole scalp. Overdoing it might not fetch good results. Also, after applying the oil to your scalp, leave it on for a few hours.
4) Use the oil two to three times a week for about six months to meaningfully track the oil's effectiveness on your head. 
5) Do not use rosemary oil if you are breastfeeding or pregnant. Certain 100% rosemary products can also lead to miscarriage or affect the health of the fetus. 
6) Rosemary hair care products cannot perform miracles if it's been a long time since you had hair issues. For best results, apply it within a short while of starting with the issues.