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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 compounds are a mixture of complex hydrocarbons that give the oil its aroma and potential therapeutic properties and that occasionally cause toxicity. More than 500 essential oils exist and are typically 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 regulation by the US Food and Drug Administration (FDA); therefore, there is no standard for manufacturing, leading to variability in active ingredients and adulterants with each producer. Furthermore, there is no standardized nomenclature for many of these herbs or for the exact chemical composition of a specific oil. Even with the strictest production guidelines, oils vary by the environment the plant was grown in and by part of the plant primarily used in production. Sometimes these differences are used to confer a particular property to the oil in terms of aroma or perceived 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.185 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 latter part of the 20th century, resurgence in interest and use of essential oils developed as many people deemed natural products to be safer and more environmentally benign. 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.164 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 poets ...

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