When choosing an essential oil, are a high price and a “100% natural” label useful signs of quality? For someone who enjoys fragrance, analysing what is inside a bottle before buying it is not straightforward.
A study published by Marissa Pierson and colleagues in 2021 analysed neroli, mandarin and bergamot essential oils purchased mainly online. The researchers asked whether their composition matched the named oils, whether they had been diluted, and whether price provided a guide to quality. The study focused on consumers’ difficulty in detecting discrepancies between labels and contents.
Examining composition, not fragrance preferences
The study concerned three citrus-derived essential oils. Neroli is distilled from bitter orange flowers, while mandarin and bergamot oils come from the peel. The researchers selected commercial samples to cover a broad price range and also analysed reference samples obtained from fragrance companies.
The main method was gas chromatography. Constituents of a mixture are separated in sequence, identified using mass spectrometry and other techniques, and compared by their detected proportions. Where needed, the researchers also used liquid chromatography and nuclear magnetic resonance.
They compared the oils with ranges for specific constituents in the ISO and AFNOR standards used at the time of the study. These are benchmarks for evaluating an oil’s chemical characteristics. This was not a test of which scents people prefer or whether users experienced harm.
The authors reported that more than 45% of 31 commercial samples failed to meet the standard ranges used, and more than 19% showed dilution. However, the paper contains inconsistencies in the breakdown of purchased samples and the numbering of reference samples, so these figures should be read as the authors’ reported totals. They are not estimates of non-compliance across the present-day market.
Falling outside a standard is not the same as adulteration
Some neroli samples had a high proportion of linalyl acetate and low levels of other characteristic constituents. In others, diluents such as propylene glycol and dipropylene glycol were clearly visible in the analysis.
Some neroli samples also contained substances the authors describe as synthetic fragrance materials, including ones with a neroli-like odour. The possibility that ingredients were added to adjust the scent needs to be distinguished from substantial natural variation in composition.
In some mandarin samples, limonene accounted for about 95%, and another constituent associated with mandarin’s characteristic composition was not detected. The researchers suspected substitution with sweet orange oil and reported that analysis of another group of compounds also supported that interpretation.
Other samples were only slightly outside the limits. Plant composition varies with origin, season, fruit maturity, production and storage. Mandarin materials harvested at different stages of ripeness, for example, are sold commercially, so comparison with a single standard range cannot establish that every deviation is adulteration.
The study also included a sample sold as tangerine. Even if its composition did not fit the mandarin standard, it could be consistent with the different type stated on its label. Correctly identifying what is being analysed matters before applying a standard.
An oil can have the right proportions and still be diluted
Bergamot provided a clear example of a quality-control pitfall. One sample contained a large signal from the solvent triethyl citrate. Yet when that signal was excluded and only the proportions among the remaining oil constituents were compared, they fell within the standard ranges.
Another sample also had relative constituent proportions consistent with the standard, but was judged to be heavily diluted with vegetable oil. That oil is difficult to see directly by ordinary gas chromatography; nuclear magnetic resonance revealed a pattern characteristic of soybean oil.
If all the oil constituents are diluted to the same extent, their proportions relative to one another remain unchanged. A plausible limonene-to-linalool ratio alone cannot guarantee that the entire bottle contains essential oil.
This example shows the value of combining checks of compositional ratios with tests for diluents and less-volatile constituents. A composition close to the standard and an absence of dilution are not one and the same condition.
Even the most expensive neroli failed to meet every criterion
The researchers divided the purchase price by the bottle volume and compared price per mL with the analytical results. Neroli prices varied widely in this sample set, and even the most expensive sample was outside the ranges for six of the 13 constituents specified by the standard.
The sample that met every criterion was in the middle of the sample set’s price range. Some relatively inexpensive samples also had compositions close to the standard. The authors argued that buying the most expensive product could not be assumed to solve the problem.
This does not establish the opposite ranking, with cheaper oils being better. The findings concern a limited set selected to span different prices, not a large random sample of the market. The appropriate conclusion is that price alone has little basis as a substitute for quality assurance.
Reliable labels need testing and traceability
The authors noted that many labels used expressions suggesting purity, naturalness or a therapeutic grade, but these did not in themselves guarantee agreement with the analysis. The tests also could not determine whether retailers had blended the products themselves or had received different contents from their suppliers.
The researchers emphasized supply-chain transparency and quality control. Systems that trace the origin of materials and verify whether purchased products match their labels can help compensate for consumers’ lack of analytical equipment. This does not mean that simply adding a familiar brand name is enough.
The study did not examine purchasers’ skin symptoms or effects from inhalation or ingestion. The percentage of non-compliant samples cannot be reinterpreted directly as the percentage of dangerous products. Nevertheless, discrepancies between labels and actual composition make it harder for users to know the ingredients and concentrations, which is an important reason for seeking quality control.
The work was supported by Université Côte d’Azur and the French National Centre for Scientific Research, with some research funding from Pharmapur UG. The authors stated that the company had no involvement in experimental design, analysis or presentation of the results, and declared no other conflicts of interest.
Summary
The citrus oils examined showed different problems, ranging from slight deviations from standards to evidence of diluents or other materials. High prices and the word “natural” alone did not adequately distinguish them.
An important implication is the need for supplier-side analysis and traceability to support what consumers cannot fully verify by scent or labels. Alongside ratios between constituents, testing should examine dilution and added materials, while distinguishing natural variation from inappropriate labelling. Together, these measures build confidence in essential-oil quality.
References
Pierson, M., Fernandez, X., & Antoniotti, S. (2021). Type and magnitude of non-compliance and adulteration in neroli, mandarin and bergamot essential oils purchased on-line: potential consumer vulnerability. Scientific Reports, 11, 11096. DOI: 10.1038/s41598-021-90307-2. Full original article.
Original article: © The Author(s) 2021. Published under CC BY 4.0.
