Story of Methyl Salicylate

Introduction

Methyl salicylate is the dominant compound found in both wintergreen and birch essential oils. While chemically similar, these two oils originate from entirely different botanical sources and have been historically used for various traditional purposes. In this article, we explore the chemistry, market authenticity, and quality concerns surrounding birch and wintergreen essential oils currently available on the market.

Wintergreen oil is steam distilled primarily from the leaves of Gaultheria fragrantissima and Gaultheria procumbens, while birch oil is typically derived from the bark of Betula lenta. In their natural, authentic form, both oils are primarily composed of methyl salicylate, which often constitutes 96–99% of the total composition. Despite this similarity, their aroma profiles, traditional uses, and cultural significance differ.

Traditional Usage and Aromatic Differences Historically, birch oil has been used in North America for joint and muscular applications and is culturally associated with the woodland and tree-based aroma profile. Wintergreen, on the other hand, is known for its sharp, sweet, minty scent and has been widely used in topical preparations in Asia and South America. Though the main component is the same, these essential oils are not interchangeable in practice due to their differing organoleptic and ethnobotanical identities.

Botanical Taxonomy

Wintergreen – Gaultheria procumbens

• Genus: Gaultheria Named in honor of Dr. Jean-François Gaultier (1708–1756), a physician and botanist from Quebec who extensively studied North American flora.
• Species: procumbens Derived from Latin: pro meaning “forward” and cumbere meaning “to lie down,” referring to the plant’s low, creeping growth habit.

Sweet Birch – Betula lenta

• Genus: Betula, Latin for birch, referring to the tree’s genus.
• Species: lenta Latin for “flexible” or “pliant,” likely describing the tree’s supple young twigs. (Note: Not to be confused with Betula nigra, which is river birch and not a source of methyl salicylate.)

History

The Story of Methyl Salicylate: From Forest Traditions to Synthetic Tracing

1700s – Folk Origins & Healing Roots

• Early 1700s: Native American tribes, such as the Delaware, Mohicans, and Iroquois, used Gaultheria procumbens (wintergreen) leaves to relieve discomfort, applying poultices and preparing teas to soothe head tensions, joint pain, and sore gums, as noted in Native American Ethnobotany by Daniel Moerman.
• Late 1700s: European settlers adopted wintergreen tea, believing it supported kidney function, digestion, and blood purification, an idea reflected in early pharmacognosy texts like Youngken’s Textbook of Pharmacognosy.

1800s – Commercial Use & Botanical Chemistry

• Early 1800s: Wintergreen oil entered commerce as a steam-distilled product, valued for both wellness and flavoring purposes, according to Ernest Guenther’s The Essential Oils.
• 1815: In Philadelphia, Swaim’s Panacea, a popular patent medicine, listed wintergreen oil among its ingredients, as recorded in the U.S. Dispensatory.
• 1842: French chemist Auguste Cahours identified methyl salicylate as the main compound in wintergreen and sweet birch oils, a discovery published in Annales de Chimie et de Physique.
• 1842–1890: During this period, oils from sweet birch and wintergreen were often marketed interchangeably as “oil of wintergreen.”

Late 1800s – Synthetic Development

• 1886: Chemists at the German firm Schimmel & Co. synthesized methyl salicylate, marking a shift toward industrial-scale production. This breakthrough was documented in their Semi-Annual Reports on Essential Oils.

1900s – Commercial Expansion & Adulteration

• Early 1900s: Methyl salicylate became popular in the food and pharmaceutical industries, used in candies, toothpaste, root beer, and pain-relief products—an expansion noted in Fenaroli’s Handbook of Flavor Ingredients.
• 1930s–1960s: As natural oil prices rose, synthetic methyl salicylate was frequently added to or substituted for genuine wintergreen oil. This trend was reported in the USDA Agriculture Yearbooks.
• In the 1970s, wintergreen distillation declined across the United States, with a few operations continuing in places like Shelby, North Carolina.

Modern Era – Analytical Checks & Quality Control

• 1988: PepsiCo researcher C. Frey developed a method using the selected ion monitoring method (SIM) to detect synthetic methyl salicylate. His research introduced a new standard for authenticity verification.
• Today, Nepal and China are the major producers of wintergreen essential oil. However, global demand and economic pressures continue to drive the practice of adulteration.

Left – North American (Gaultheria procumbens) Low-growing groundcover with small, rounded leaves. Native to eastern North America.

Middle – Nepalese (Gaultheria fragrantissima) Upright shrub with long, pointed leaves. Common in Himalayan forests.

Right – Chinese (G. fragrantissima or variant) Visually similar to Nepalese type. The reddish new leaves are a result of fresh growth, not a different species.

Nepalese and Chinese wintergreen are nearly identical in appearance differences are mostly seasonal or environmental.

Chemistry of North American Wintergreen (Gaultheria procumbens)

The essential oil of G. procumbens, native to eastern North America, is chemically distinct and notably different from commercially available "wintergreen" oils sold today, most of which are derived from Gaultheria fragrantissima.

An authentic essential oil from G. procumbens cultivated in southern Alabama shows the following profile:

• Methyl salicylate dominates the oil at 91.1%, as expected.
• Unique minor compounds include:

• Tuberolactone (5.3%)
• Massoia lactone (1.3%)
• (E)-Cinnamyl alcohol (0.8%)
• Thymol (0.3%)

These lactones and cinnamic derivatives are rarely reported in G. fragrantissima, making them valuable chemical markers for distinguishing G. procumbens oil.

Methyl Salicylate is a Product of the Gaultherin hydrolysis in Birch or Wintergreen essential oils.

In Gaultheria species such as wintergreen and birch, methyl salicylate is not present in free form. Instead, it exists as gaultherin, a glycoside where methyl salicylate is bound to primeverose. During steam distillation, the enzyme gaultherase becomes active in the presence of water, hydrolyzing gaultherin and releasing methyl salicylate. Thus, the characteristic wintergreen aroma is not pre-formed in the plant, but biosynthetically liberated during distillation.

Synthetic Methyl Salicylate & Its Marker: A Chemical Trace

Methyl salicylate, when produced synthetically, is typically derived through a multi-step chemical process starting from phenol. Phenol is first converted into salicylic acid, which is then methylated to form methyl salicylate. During this synthetic route, especially when industrial reagents and solvents are used, trace by-products such as dimethyl 2-hydroxyterephthalate may form, compounds that do not occur naturally in Gaultheria-derived essential oils. These by-products act as synthetic markers or “chemical fingerprints” of industrial origin.

In Frey’s 1988 study, dimethyl 2-hydroxyterephthalate was identified as a reliable synthetic marker. The GC-MS chromatogram shows methyl salicylate as a significant peak. At the same time, the synthetic marker appears later with a distinct retention time and its characteristic mass fragmentation pattern, including key ions at m/z 119, 147, 178, and 210. These marker peaks are absent in genuine wintergreen essential oil distilled from plant sources, making them necessary for detecting adulteration or confirming synthetic origin.

Marker-free 100% synthetic wintergreen EO

This radiocarbon (C14) analysis reveals a completely reconstructed wintergreen oil that superficially mimics a natural essential oil. The GC-MS profile shows no detectable synthetic marker (SM), such as dimethyl 2-hydroxyterephthalate, which typically signals industrial origin. However, carbon isotope analysis revealed that the sample contained only 1% biobased carbon, confirming that the material is over 99% fossil-derived, indicating that it is synthetic. This suggests that the manufacturer likely added trace amounts of natural plant-derived compounds such as linalool, thymol, or limonene to create a sensory illusion of authenticity, thereby evading marker-based detection. Despite its “natural” aroma and clean chromatogram, this oil is not truly natural. It is fully synthetic in composition, disguised through booster molecules and marker-free synthesis.

How did they make marker-free synthetic wintergreen?

When I first encountered a marker-free synthetic wintergreen oil, its GC-MS profile showed no signs of known synthetic by-products, such as dimethyl 2-hydroxyterephthalate. Even though it mimicked a natural essential oil chromatographically, C14 radiocarbon testing revealed just 1% biobased carbon, proving it was almost entirely fossil-derived. This raised an important question: how was it made to appear so natural? To explore this, our EO adulteration research group synthesized methyl salicylate from expired aspirin, following a two-step process: hydrolysis of acetylsalicylic acid to salicylic acid, followed by acid-catalyzed esterification with methanol. The result was a high-purity synthetic product chemically identical to natural wintergreen oil and devoid of the common industrial markers in standard GC-MS.

However, with the advancement of tools, my lab now utilizes tandem mass spectrometry (GC-MS/MS) to dig deeper. Using this method, we can detect synthetic markers at parts-per-billion (ppb) levels, even when they evade conventional detection. As shown in the latest chromatograms, even reconstructed or ultra-purified oils that previously passed as natural can now be exposed.

Market survey of Wintgereen and Birch EO

• Over 80% of commercial wintergreen essential oils were found to contain synthetic methyl salicylate, either partially or entirely. This conclusion came from a survey of products from 50 leading essential oil companies.
• We analyzed 27 commercial birch essential oil samples from reputable suppliers and found none contained true birch oil. Most were either wintergreen, a blend of synthetic and natural wintergreen, or pure synthetic methyl salicylate. Since birch oil production ended in North America around the 1970s, this result, though alarming, is expected.

How did we know none of them were true Birch EOs?

How did we know none of the samples were true birch essential oils? Differentiating pure birch oil from wintergreen oil is challenging using standard lab testing methods. To address this, we conducted several lab-scale distillations of known birch bark and analyzed them to identify unique chemical markers. Based on those controlled distillations, we identified key birch-specific biomarkers that are absent in wintergreen oil. When we compared these markers to the commercial samples labeled as birch, none of them contained any of these markers, confirming that none were true birch essential oil.

Since birch essential oil is derived from the bark of the tree, we collected and analyzed samples from 34 different birch trees sourced from various regions around the world. This helped us establish reliable biomarkers, such as 2-trans-4-cis-decadienal, which are characteristic of authentic birch oil.

In conclusion, birch oil typically contains more salicylate esters (including compounds beyond just methyl salicylate, such as ethyl salicylate), along with a higher abundance of aliphatic aldehydes and phenolic compounds. In contrast, wintergreen oil is dominated by terpenes, including both monoterpenes and sesquiterpenes, which can be present in birch oil but in tiny quantities. These chemical differences make it possible to distinguish true birch oil from wintergreen when proper analytical methods are used.

Final Thoughts for Buyers and Brands. If a supplier claims to sell authentic birch essential oil, responsible due diligence involves asking for details such as:

• Source of the raw material (region, plant species)
• Distillation facility information
• Photos or documentation of bark collection and distillation
• GC-MS reports that include minor compound profiling

True transparency should be welcomed, not shied away from.

Conclusion: Although methyl salicylate is the main compound in both birch and wintergreen oils, their authenticity, aroma, and traditional use set them apart. In an industry where visual inspection alone is insufficient, scientific testing and ethical sourcing play a crucial role in ensuring quality and integrity. As professionals and consumers, we must demand clarity, not just chemistry.

#EssentialOils #MethylSalicylate #BirchOil #WintergreenOil #AuthenticityMatters #GCMSTesting #TransparencyInBusiness

By Dr. S