One of the ways rosemary oil stimulates hair growth is by causing blood vessels to dilate, according to GlobalPost. The oil triggers the hair follicles to begin growing hair by promoting increased scalp circulation.
Although rosemary oil can be used alone, the website recommends blending it together with other essential oils such as grapeseed, jojoba, lavender, cedarwood or thyme. The site suggests thoroughly massaging the scalp with the treatment. A recipe is also available for a homemade rosemary oil scalp treatment.
This oil is vital in promoting hair growth, because it increases the flow of blood circulation to the head and scalp area, according to about.com.