There is the water extract or the essential oil that is commonly used. Rosemary oil is the one people generally refer to when it comes to haircare as it has the strongest properties. However, there are many ways to incorporate it into your routine depending on what you’re trying to achieve so I unfortunately don’t have an easy ‘yes/no’ answer ? You can use it for example a few drops in your homemade shampoo for scent and antimicrobial purposes, which will help improve your scalp health without big risks or downsides. For more intensive care, you can for example apply it directly on the scalp (diluted with water or oil) to help your scalp health. But again, it works wonders for some scalp issues but not all. So the most important thing when it comes to scalp treatments is to understand clearly what you want to improve and what is the cause of your issue before choosing a treatment. For example, itchiness can be caused by dryness or excess oil on the scalp. The treatment whether you have one or the other will be completely different so it’s hard for me to tell you if rosemary oil will benefit you without knowing your personal situation.