Essential oils are composed of molecules of aromatic compounds. One essential oil might contain hundreds of these aromatic compounds, which contribute to the oil’s unique aroma and physiological actions. Chemists call these “volatile compounds” because their molecules easily evaporate, or volatilize, into the air. This is contrasted with fixed oils, such as cooking oils, which do not evaporate as quickly.
Essential oils can enter your body via absorption through your skin. In addition, the aromatic molecules floating around in the air enter your nose and are picked up by olfactory receptors. These transport information to the olfactory bulb located at the top of the nasal passage at the base of your brain. From there, scent information is passed on to the limbic system, a primitive part of your brain responsible for very basic body functions. The limbic system communicates with the hypothalamus and pituitary, master glands that affect and regulate fundamental body processes including the secretion of hormones and the regulation of moods, digestion, appetite, sexual arousal, and heartbeat. Aromas also stimulate the parts of your brain that control memory.