Essential oils are most commonly used in the practice of aromatherapy. They are either inhaled or diluted then rubbed on the skin. Essential oils can be ingested orally however this method is not advised. The active chemicals in essential oils can interact with your body in a number of ways.
Apple topically, the oils are absorbed just like the ingredients in common pharmaceuticals such as hormone replacement therapy cream or nicotine patches. Inhaling the aromas from essential oils can stimulate areas of your limbic system, which is a part of your brain that plays a role in emotions, certain behavior, sense of smell and long-term memory. Interestingly, the limbic system is heavily involved in forming memories. This can partially explain why familiar smells can trigger memories or emotions.
The limbic system also plays a role in controlling some unconscious physiological functions, such as breathing, heart rate and blood pressure. Some people claim that essential oils can exert a physical effect on your body in this way. However, this has yet to be confirmed in studies.