The Essence of Essential Oils

Essential oils (liquid mixtures of volatile compounds) isolated from numerous aromatic plants have been used for several centuries by various civilizations as cosmetics, perfumes, preservatives, and medicines. Indeed, these substances have long been used in traditional medicine and, more recently, become known to confer antioxidant, anti-inflammatory, and antimicrobial effects to several cosmetic formulations. Essential oils are used in modern skin care as pressed plant extracts mainly to add fragrance or added to skin care formulations to mask unpleasant aromas. They are also used as oils, preservatives, and penetration enhancers in numerous skin care products. In addition, essential oils are incorporated into air fresheners as well as candles and used in aromatherapy and massage oils. The benefits of these ingredients depend on the plant from which they are derived and how they were extracted. This column provides a brief overview regarding the benefits of essential oils in dermatology.

Components

In a 2010 review, Miguel noted that while essential oils are typically characterized by an elaborate array of constituents, ranging from dozens to hundreds, most components include terpenes (oxygenated or not), with monoterpenes and sesquiterpenes the most common, as well as allyl- and propenylphenols (phenylpropanoids) also appearing as significant ingredients. The terpenes are created through the mevalonate pathway, and phenols emerge through the shikimate pathway. Some alcohols, ethers, ketones, and aldehydes (such as linalool, 1,8-CineoIe, geranial and neral, citronellal, isomenthone, menthone) and monoterpenes (alpha-terpinene, beta-terpinene and alpha-terpinolene) in essential oils are thought to specifically contribute to the antioxidant properties of these compounds. 

It is important to note that essential oils are extracted from one plant at a time. Further, not all plant extracts are classified as essential oils, not all plants provide essential oils, and essential oils are not always oils, as several lack fat content and/or glycerol. Such “oils” that are not true oils cannot hydrate the skin or strengthen the skin barrier. Further, some essential oils provide no useful applications beyond fragrance. 

Extraction and Processing

Essential oils are extracted from the leaves, roots, flowers, barks, stems, fruits, or other parts of the plant through mechanical expression (without heating, for citrus fruits), steam distillation, or pressure processing. Genuine plant oils are typically obtained through expression or pressing (eg, olive oil). This allows them to retain fatty acids and other key substances that are removed through steam distillation and pressure processing. An initial pressing leaves more active ingredients than subsequent ones. Notably, extra virgin olive oil is derived from the first pressing, yielding a higher level of antioxidants than later pressings. The type of extraction process clearly influences the benefits, components, and activities of the final essential oil. 

Several essential oils do not contain lipids and fail to meet the scientific definition of oils due to steam distillation or pressure processing. Some essential oils do contain fats and are, therefore, deemed real oils. The benefits that such oils impart to the skin are influenced by their individual fatty acid content. Essential oils containing lipids are either saturated or unsaturated, depending on the chemistry of the plant of origin. Sunflower seed oil, which contains unsaturated fat, is a good example of an essential oil used in skin care. 

In addition to the processing used to obtain a functioning essential oil, the anti-inflammatory, antioxidant, photosensitizing, and allergenic actions of an essential oil also depend on the plant, where it is grown, and soil characteristics. Thus, its efficacy can vary from season to season and is susceptible to the effects of climate change. 

Anti-inflammatory Activity

Several essential oils have been found to deliver anti-inflammatory activity, with chamomile essential oil known for hundreds of years to be effective in treating eczema, dermatitis, and other skin irritations, as well as essential oils of eucalyptus, rosemary, lavender, and millefolia, for example, used as anti-inflammatory agents. Other essential oils commonly used in skin care products include argan oil, bilberry seed extract, Chinese lizard tail, evening primrose oil, lemon peel oil, olive oil, rose oil, safflower oil, sunflower oil, and Ulmus davidiana root (also known as yugeunpi). 

In 2016, Ndoye Foe et al. characterized the antioxidant and anti-inflammatory effects of the essential oils of four dietary and medicinal plants (Drypetes gossweileri, Pentadiplandra brazzeana, Allium cepa,Alium sativum) from Cameroon. Analysis of the essential oils revealed that all had copious phenolic components (A. sativum < A. cepa < D. gossweileri < P. brazzeana). The DPPH radical scavenging test revealed that all of the oils displayed robust antioxidant activity. Each essential oil was also found to demonstrate notable anti-inflammatory properties. The authors attributed the significant antioxidant and anti-inflammatory effects of these essential oils to the abundant supply of organosulfur constituents present. These activities, they concluded, suggest that the essential oils may warrant inclusion in cosmetic products. 

Notable anti-inflammatory activity has also been reported in association with the essential oil of Melaleuca alternifolia (better known as tea tree oil) and is attributed to its key constituent alpha-terpineol. 

Antioxidant Activity

In 2019, Valdivieso-Ugarte et al. reported on their systematic literature review in PubMed, Embase, and Scopus conducted from 2014 to 2019 using various combinations of these keywords: “essential oils, volatile oils, antimicrobial, antioxidant, immunomodulation, and microbiota.” The authors noted that multiple studies have demonstrated that essential oils deliver healthy benefits by virtue of their varied biological functions, including antioxidant, anti-inflammatory, antimicrobial, and immunomodulatory activities, though their aromas can hinder their inclusion in some skin care products and enhance others. 

In a 2020 review of some spices used in traditional medicine, specifically Cinnamomum zeylanicum (true cinnamon), Mentha piperita (peppermint), Ocimum basilicum (basil), Origanum vulgare (oregano), Piper nigrum (black pepper), Rosmarinus officinalis (rosemary), and Thymus vulgaris (thyme), authors reported that the essential oils of each plant demonstrated significant antioxidant activity. 

The next year, Guo et al. analyzed the absolute antioxidant activity of five phenol-rich essential oils: the terpene-rich T. vulgaris, O. vulgare, and Satureja hortensis, as well as phenylpropanoid-rich Eugenia caryophyllus and C. zeylanicum. All the essential oils were found to impart antioxidant protection of cumene, with duration commensurate with phenolic content, and substantial protection of squalene. The researchers also determined that each essential oil would be eligible to replace synthetic butylated hydroxytoluene to protect cosmetics and food products. 

Overall, the essential oils considered to exert the most robust antioxidant activity are those of basil, cinnamon, clover, nutmeg, oregano, and parsley, with thymol and carvacrol found to be the most active constituents. 

A Note on Nomenclature

Essential oils are called just that because they are thought to convey the “essence” of the original plant. It is used to describe pressed plant extracts and makes no reference to fat content. The expression and these oils should not be confused with “essential fatty acids,” which cannot by synthesized by the human body and are essential for good health. The majority of essential oils are not true oils because they contain no fatty acids. 

Essential oils are typically flammable, like most other oils. Sometimes, but not always, essential oils manifest a hydrophobic quality like normal oils. Notably, essential oils that do not qualify as genuine oils can provide benefits, such as antioxidant or anti-inflammatory activity, to the skin. 

Conclusion

Essential oils are known to impart antioxidant, anti-inflammatory, antimicrobial, and other functions beneficial to health and are useful in various medications and other products developed to treat the skin. These plant-derived products are important in dermatology because of their use in cosmetics, preservatives, fragrances, and other skin care products. 

Dr Baumann is a private practice dermatologist, researcher, author, and entrepreneur in Miami. She founded the Division of Cosmetic Dermatology at the University of Miami in 1997. The third edition of her bestselling textbook, Cosmetic Dermatology, was published in 2022.