Essential oils

The American Heritage Dictionary defines essential oil as:

A volatile oil, usually having the characteristic odor or flavor of the plant from which it is obtained, used to make perfumes and flavorings.

Familiar examples of essential oils include those extracted from species of citrus, lavender, seeds of celery and pumpkin, eucalyptus, and rosewood.

In addition to their use in perfumes and flavorings, essential oils have been used in complementary and alternative medicine as antimicrobials. Microbiologists Hammer and colleagues studied the in vitro antimicrobial activity of 52 essential oils, reporting as follows:

In summary, this study confirms that many essential oils and plant extracts possess in vitro antibacterial and antifungal activity. However, if plant oils and extracts are to be used for food preservation or medicinal purposes, issues of safety and toxicity will need to be addressed.

Aromatherapy

The odoriferous quality of essential oils lends itself to the practice called aromatherapy, wherein the inhalation of the odors of an oil may yield positive health effects of various types. The National Cancer Institute (NCI), linked through the National Center for Complementary and Alternative Medicine (NCCAAM), provides the following overview of aromatherapy for health professional:

• Aromatherapy is the therapeutic use of essential oils (also known as volatile oils) from plants (flowers, herbs, or trees) for the improvement of physical, emotional, and spiritual well-being.
• Aromatherapy is used by patients with cancer primarily as supportive care for general well-being.
• Aromatherapy is used with other complementary treatments (e.g., massage and acupuncture) as well as standard treatment.
• Essential oils are volatile liquid substances extracted from aromatic plant material by steam distillation or mechanical expression; oils produced with the aid of chemical solvents are not considered true essential oils.
• Essential oils are available in the United States for inhalation and topical treatment. Topical treatments are generally used in diluted forms.
• Aromatherapy is not widely administered via ingestion.
• The effects of aromatherapy are theorized to result from the effect of odorant molecules from essential oils on the brain’s emotional center, the limbic system. Topical application of aromatic oils may exert antibacterial, anti-inflammatory, and analgesic effects.
• Studies in animals show sedative and stimulant effects of specific essential oils as well as positive effects on behavior and the immune system. Functional imaging studies in humans support the influence of odors on the limbic system and its emotional pathways.
• Human clinical trials have investigated aromatherapy primarily in the treatment of stress and anxiety in patients with critical illnesses or in other hospitalized patients. Several clinical trials involving patients with cancer have been published.
• Aromatherapy has a relatively low toxicity profile when administered by inhalation or diluted topical application.
• Aromatherapy products do not need approval by the U.S. Food and Drug Administration because there is no claim for treatment of specific diseases.
• Repeated exposure to lavender and tea tree oils by topical administration has been associated with reversible prepubertal gynecomastia.

Production

Distillation

See also: Distillation

Some common essential oils, such as lavender, peppermint, tea-tree and eucalyptus, are distilled. Raw plant material, consisting of the flowers, leaves, wood, bark, roots, seeds, or peel, is put into an alembic (distillation apparatus) over water. As the water is heated the steam passes through the plant material, vaporizing the volatile compounds. The vapors flow through a coil where they condense back to liquid, which is then collected in the receiving vessel.