Gandha-Chikitsa (Aroma-therapy) is an ancient practice, where spirit of Plants (Essential oils) are inhaled/applied on the body, aroma molecules of essential oils are sensed by Olfactory part of the brain and instantly regulates disturbed involuntary functions and nervous system of the body by regulating necessary hormone secretions and accelerating inter-cellular communication in the body.
Dhyana Yoga incorporates "Aroma-Therapy" in the meditation, where essential oils are applied on certain energy nodes of the body or diffused in the air, which helps to ground the disturbed mind quickly by relaxing the nerves and helps to focus on the meditation by easing the energy/Prana flow.