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Essential oils are a class of volatile oils that are extracted through steam distillation or are cold pressed from the leaves, flowers, bark, wood, fruit, or peel of a single parent plant. The term essential refers to the essence of a plant, rather than an indispensable component of the oil or a vital biologic function. These organic compounds are a mixture of complex hydrocarbons that give the oil its aroma, therapeutic properties, and occasionally cause toxicity. More than 500 essential oils exist and can be categorized into five chemical groups: terpenes, quinines, substituted benzenes, aromatic/aliphatic esters, and phenols and aromatic/aliphatic alcohols.


The potential for toxicity arises from several aspects of oil production, use, and regulation. These oils are not under the US Food and Drug Administration (FDA) regulation; therefore, they may not contain the specific ingredient intended for use or may contain excessive amounts of the active ingredient, other chemicals, or various adulterants. Furthermore, there is no standardized nomenclature for many of these herbs or for the exact chemical composition of specific oil. Even with the strictest production guidelines, oils can vary by the environment the plant was grown in and by part of the plant primarily used in production. Sometimes these differences are utilized to confer a particular property to the oil in terms of aroma or believed therapeutic benefit.

Therapeutic use of essential oils can be traced back thousands of years in history to the ancient Greeks and ancient Egyptians, and it is also described in biblical writings. The first documents detailing an actual distillation process date back to the ninth century, when such oils were imported into Europe from the Middle East.158 By the 16th century, concepts of separating fatty oils and essential oils from aromatic water became more defined, and oils were used frequently for fragrance, flavoring, and ­medicinal ­purposes. By the 19th century, these processes became industrialized, and specific chemicals could be identified and mass produced. Essential oils fell out of favor in the early 20th century, as new medications and a desire for modernization developed. However, in the past 30 years, resurgence in interest and use of essential oils developed as many people deemed natural products to be safer and more environmentally friendly. This chapter highlights some of the most commonly used oils for medicinal purposes that also have the greatest potential for toxicity.




Artemisia absinthium is more commonly known as wormwood because of its use as an anthelmintic in ancient times. It is a member of the Compositae family, which also includes ragweed, chrysanthemums, marigolds, and daisies.139 Absinthe is a liqueur composed of ethanol, oil of wormwood, and various other herbs, and it is known for its green color and bitter taste. It became a favorite among the artists and ...

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