Essential oils contain the essence of the plant’s fragrance.  The oil is isolated by a physical process from an odoriferous plant and bears the name of the plant from which it is derived.  Essential oils are primarily intended for aromatherapy, or as a fragrance or scent by diffusion into the air.  Certain essential oils are suitable for external use, but they need to be used with great care due to their highly concentrated nature and their reaction to sunlight.