The advantage of these oils comes from their in fluence on the limbic system, which coordinates mind and body activity. This system is very sensitive to odors and encodes them into associations and memories, which when awakened alter basic physical functions such as heart rate, blood pressure, breathing, and hormone level. When these oils are rubbed into the skin or inhaled, they set off a reaction leading to rapid and significant alterations in memory, heart rate, and other bodily mechanisms. Some boost energy, some promote relaxation, and others have pharmaceutical effects. However, no treatment should ever involve more than a few drops of oil.