An essential oil, also known as volatile oil and ethereal oil, is a water-immiscible liquid produced by distillation from plant material that is used in perfumes, cosmetics, incenses, and in medicine.
The raw material (flowers, leaves, stems, or roots, seeds, or seed peel, depending on the plant) is put in an alembic over water, and the volatile compounds, which require less vapor pressure to evaporate with the presence of steam, distill into a receiving vessel. The upper portion is the oil, the lower being the hydrosol. Most oils are distilled in a single process. The exception is ylang-ylang, which takes 22 hours to complete distillation. It is fractionally distilled, producing several grades.
Many vendors sell fragrance oils which are blended synthetic aroma compounds or essential oils diluted with a carrier like propylene glycol, vegetable oil, or mineral oil.
Many essential oils have medicinal properties that have been applied in folk medicine since ancient times and are still widely used today. For example:
Tea tree oil, leleshwa oil, sandalwood oil, and many other essential oils have topical (external) antimicrobial (i.e. antibacterial, antifungal, antiviral, or antiparasitic) activity and are used as antiseptics and disinfectants.
Clove oil is a topical analgesic, especially useful in dentistry. It is also used an antiseptic, antispasmodic, carminativum, and antiemetic.
Lavender oil is used as an antiseptic and for a number of other folk medicinal uses.
Yarrow oil is used to reduce joint inflamation and relieve cold and influenza symptoms.
- Plai oil (a species of ginger) is also used for treating joint pain.
Aromatherapy is a form of alternative medicine, in which healing effects are ascribed to the smell of particular fragrances.
Prior to the discovery of distillation essential oils were extracted by pressing, and this is still the case in cultures such as Egypt. Traditional Egyption practice involves pressing the flower and then burying it in unglazed ceramic vessels in the desert for a period of months to drive out water. The Lotus oil retaining its scent after 3000 years in alabaster vessels in Tutankhamun's tomb was pressed, rather than distilled.
The smoke from burning essential oils may contain dangerous cancer producing products, such as polycyclic aromatic hydrocarbons (PAHs). The essential oils themselves are volatile organic compounds (VOCs).