Essential oils are compounds extracted from plants through distillation via steam and/or water, or mechanical methods, such as cold pressing. Cold pressing is most commonly used to obtain essential oils from citrus fruits such as oranges, bergamot, grapefruits, lemons, and limes. The oils capture the plant's unique scent and flavour, or "essence." In ancient times, essential oils were known as the soul of the plant. 

Ancient Egypt was the true birthplace of essential oils. The Egyptians cultivated plants for their oils and used them extensively in their religion, in cosmetics, as well as for medicinal purposes.  Aromatic essence and resins were also used in the embalming process.  China and India were exploring herbs and aromatic plants too, which would become an integral part of the Indian Ayurvedic medical system. 

Essential oils are volatile in nature and evaporate quickly. When the essential oils particles are inhaled, they travel up the nasal passageway to the lungs and the olfactory system of the brain. The olfactory system is what controls our sense of smell. The olfactory receptors send signals to the part of the brain called the limbic system. The limbic system is known as the emotional brain because it forms and stores memories. Essential oils largely affect the hypothalamus and pituitary gland which are part of the limbic system and are responsible for sleep and hormonal balance. When used topically, the essential oils are absorbed via the pores in the skin and affect the surrounding muscles and tissues. They then seep into the bloodstream and lymphatic system, and from there reach all the internal organs. Once their work is done, the oils are excreted via the lungs, kidneys and skin. Because of the ability of these oils to enter the bloodstream and parts of the brain so rapidly, they have a huge impact on many different areas, ranging from emotions, to hormonal imbalance, and aches and pains.