Definitly dilute it first before putting it on your scalp. Rosemary is quite a stimulating oil and may not be the best oil to use immediately before going to bed. See how you get on with it. There are other good essential oils too which could be useful such as roman chamomile, lavender, basil, geranium, clary sage, thyme and cedarwood, although it does depend on the reason for the hair loss. Mustard oil and sesame oil are both good hair oils too. Whichever oil you use, make sure you massage your scalp well as it will help improve the circulation to the scalp which can help encourage new hair growth.