Essential oils are a marketing marvel!

This post give practical tips on how essential oils are handled in chemical regulations, particularly for hazard classification, labelling, and safety data sheets (SDSs). Labelling is explained for chemical products, detergents, biocides, and cosmetics.

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What are essential oils?

Essential oils are a marketing marvel! The name conjures a picture of natural fragrance that can bring wonder to everyday products – air fresheners, detergents, and cosmetics. The exotic world brought into the household.

As a chemist, responsible for the assessment of the hazards of such products, my view is more prosaic.

Essential oils are natural complex substances, comprising a mixture of chemical components. Each component may present physical, toxicological and environmental hazards. The composition of the mixture and therefore the hazard can vary depending on its source, treatment, and handling.

Essential oils are fragrance products, with a complex composition, obtained from a plant raw material by steam distillation or a simple mechanical process. Distillates are separated from the water by processes that do not affect their composition [1]. However, the supplier may use further treatments to alter the composition and characteristics of the essential oil.

The process of obtaining essential oils distinguishes them from absolutes and concretes that are derived using solvent extraction, which can produce higher concentrations of fragrance components in the mixture.

Characteristics of an essential oil

A particular essential oil is defined by:

• botanical source (species and part of the plant, and geographical source)
• processing (eg steam or dry distillation, and any further processes)
• composition (ie identity of components).

There is practically an infinite number of combinations of the these factors.

Extracts from the same species, but different parts of the plant (eg peel vs leaf) may have different compositions. Conversely, extracts from different plant species may have similar compositions (eg orange oil vs grapefruit oil).

Names and identification numbers

The names of essential oils can be confusing. They usually indicate the botanical source, sometimes the processing, and occasionally the composition. For example, there are many variations on orange oil:

• botanical source: orange peel oil, sweet orange extract, citrus aurantium leaf oil
• processing: concentrated sweet orange oil, acidified sweet orange oil, hydrogenated orange seed oil, hydrolysed orange root extract.
• Composition: sweet orange terpenes, orange seed oil unsaponifiable, mentha-1,8-diene.

Because it is difficult to capture these variations in a short name, the regulation of such chemicals usually includes a longer, more specific description in order to define the essential oil. For example, one variation of orange essential oil can be described as:

• extractives and their physically modified derivatives such as tinctures, concretes, absolutes, essential oils, oleoresins, terpenes, terpene-free fractions, distillates, residues, etc., obtained from Citrus sinensis, Rutaceae

Further confusion is caused by influential organisations using different naming conventions. REACH (1907/2006 [2]) and the CLP Regulations (1272/2008 [3]) are based on IUPAC and CAS names. Cosmetic ingredients are named according to the International Nomenclature of Cosmetic Ingredients (INCI) [4]. These conventions produce informative names, but they may be complicated and thus meaningless to consumers. Using a simplified name may be helpful.

For ease of reference, essential oils have identification numbers. For regulatory purposes, the best known of these are:

• CAS numbers
• For EU and UK, EC numbers

The CAS number may be generic and cover many variations of an essential oil. Or it might be very specific, for example when a supplier obtains a new CAS number for a product if they wish to establish it as a novel ingredient.

The EC number is generally more useful in specifying an essential oil. Many new EC numbers were created during the REACH registration process, because suppliers had to be more rigorous in identifying their essential oil substances. But often older, obsolete EC numbers are used by suppliers on labels and in safety data sheets. EC numbers are only valid in the EU and UK.

Grades

The supplier of essential oils may be supplying a very specific product for fine fragrance use, with strict quality control on the sources, processing and storage of their product to give a consistent odour and composition.

For industrial products, eg orange oil as a degreaser or as a fragrance in cleaning agents, such rigorous quality control is unnecessary.

In these two cases, the name and identification numbers of the essential oil may be the same. If you are buying essential oils, it is important to understand the variations in product quality and composition to make sure they are suited to your purpose.

Many essential oils are known to oxidise if stored in poor conditions. This can affect the composition of the essential oil to the extent that new hazards are created. Limonene, a common component of citrus essential oils, can be oxidised during storage to products that cause skin sensitisation.

Regulations and essential oils

In EU and UK legislation, particularly REACH and the CLP Regulations, chemical products are either:

• substances [monoconstituent; multiconstituent; or substances of unknown, variable complex, or biological composition (UVCB)]  
• mixtures (deliberate combination of substances)
• articles (products where the shape is more important than the chemical composition.

For REACH and CLP Regulations, essential oils can be regarded as UVCB substances. They are registered under the REACH Regulation and have their own EC numbers.

Many applications for essential oils, for example in candles, diffusers, and household fragrances use blends of essential oils to achieve a desired fragrance. In these cases, the essential oil can be considered as a substance, and appear on the label and in the safety data sheet.

Cosmetics and detergents regulations require that certain components of essential oils are listed on the labels of these products. It is therefore necessary to have information on the components of essential oil when they are used for these purposes.

Consumers who know the specific components to which they are allergic can read the labels and avoid products that might cause them to have an allergic reaction. It is more useful to the consumer to see the name of the components than the name of the essential oils that may contain the component.

There is a need for cosmetics and detergents to be labelled in this way because of the high skin exposure to these products.

Classification of essential oils

Chemical classification is a shorthand description of the hazards of a product, and the cornerstone of chemical hazard communication, as expressed in safety data sheets and on labels.

A compendium of chemical hazards, some not covered by the CLP, is given here. We also have a useful glossary of technical terms.

The Classification, Labelling and Packaging (CLP) Regulation specifies the criteria for the classification of hazardous properties of chemical products in the EU, and the symbols and text required on the label to warn and instruct users of the product.

Substances

The classification of substances is described in detail in an earlier post.

For a single essential oil, the classification should be provided by your supplier on the SDS. You can check that the classification is correct by comparing with the freely available data on the ECHA ‘Search for Chemicals’ facility, either in the REACH Registration dossier or in the Classification and Labelling Inventory.

For example, orange, sweet, ext. (CAS 8028-48-6, EC 232-433-8) has a listed hazard classification of:

• Flammable Liquid, Category 3 (flammable liquid and vapour)
• Skin Irritation, Category 2 (causes skin irritation)
• Skin Sensitisation, Category 1 (may cause an allergic skin reaction)
• Aspiration Toxicity, Category 1 (may be fatal if swallowed and enters airways)
• Aquatic Chronic, Category 2 (harmful to aquatic life with long lasting effects).

Such hazards are typical of an essential oil, particularly those relating to skin sensitization and chronic (long-term) toxicity to aquatic creatures.

If we know the composition of the essential oil, either from the supplier SDS or from literature sources, we can check the components that are responsible for the hazards.

Again, using orange oil as an example, the components are typically:

• limonene (CAS 5989-27-5, EC 227-813-5), 90%
• myrcene (CAS 123-35-3, EC 227-813-5), 2%
• pinene (CAS 80-56-8, EC 201-291-9), 2%
• others, each less than 1%.

By checking the hazards of these components, we can see that the hazards of the orange oil are attributable to the limonene content.

Mixtures

The classification of mixtures is described in detail in an earlier post.

Household fragrance products such as scented candles and diffusers are comprised of a base substance (eg wax or glycol) and essential oils or other fragrances. Classification of the products can be calculated from the hazards of each ingredient and its percentage in the formulation.

As discussed, essential oils can be regarded as substances and the calculation can be made based on the classification of the essential oils in the base material.

However, this may lead to a more severe classification of the product than necessary, as the concentration of the essential oil is greater than the components.

For example a product containing 1% of the ‘orange, sweet, ext.’ would need the Skin Sensitisation, Category 1 classification. But by using the concentration and classification of the essential oil components, there is no skin sensitizing component present at ≥ 1%, so the the product would not require this classification.

However, if multiple essential oils contain the same component, then it is also possible to under-classify the product. If a component is present in more than one essential oil, it could be present at a higher concentration than any individual essential oil.

So a better, more accurate method is to calculate the percentage of each of the essential oil components within the product. If there is more than one essential oil present in a mixture, with the same components, then the concentration of each component should be summed.

Usually, the components of the essential oils or fragrance mixture are listed in the supplier SDS, Section 3, because of the requirement to put certain ingredients on the label for cosmetics and detergents, as discussed earlier, but there is no legal obligation to do so. Sometimes the components of an essential oil or fragrance are given in a separate ‘INCI declaration’.

Major components of an essential oil can be found from literature sources. However, because of the natural variation in components of essential oils, the supplier composition data should be more reliable.
We there recommend using the supplier information for the calculation of product mixture classification.

Labelling of products containing essential oils

CLP Regulation

To ensure correct labelling of products, you must be clear which regulations apply. The CLP Regulation applies to general chemical products that do not have specific requirements of their own.
This includes product mixtures such as:

• candles
• diffusers
• home fragrances
• fabric fresheners.

A detailed guide to product labelling according to the CLP Regulation is given on our resources page.

The CLP Regulation gives the requirements for labelling substances and mixtures.

Neat essential oils are regarded as substances, and are identified on the label with a chemical name (eg IUPAC or CAS) and an identification number (eg EC or CAS).

The sweet orange extract can be identified on the essential oil label as ‘orange, sweet, ext. (EC 232-433-8)’.

For mixtures containing essential oils, only those ingredients contributing to the classification of the product in the following Hazard Classes are declared on the label: acute toxicity, skin corrosion or serious eye damage, germ cell mutagenicity, carcinogenicity, reproductive toxicity, respiratory or skin sensitisation, specific target organ toxicity (STOT) or aspiration hazard.

For essential oils, the most common Hazard Class causing the oil to require listing on the label is skin sensitisation. Note that ingredients contributing to the product classification in ecological hazards do not need identification on the product label.

If the essential oil has been used to calculate the hazard classification of the product, and it contributes to the classification of the product in the above Hazard Classes, then the name of the essential oil should appear on the label, eg ‘contains orange, sweet, ext.’

If the classifier has used a component of the essential oil to calculate the hazard classification of the product, and it contributes to the classification of the product in the above Hazard Classes, then the name of the component should appear on the label, eg ‘contains d-limonene’.

Biocides

Biocides are regulation in the EU and UK through the Biocides Regulation (528/2012) [5]. Biocidal products are labelled according to CLP Regulation, but there are additional labelling requirements. Identification of essential oil in the biocide follow the same rules as the CLP Regulation, but with additional information needed if the essential oil is the active ingredient.

Detergents

EU or UK Detergents Regulation (648/2004 ) [6] encompasses a wide variety of cleaning products.

Detergents are labelled according to CLP Regulation, but there are additional labelling requirements.

Fragrance agents should be identified in an ingredients list as ‘parfum’.

Additionally, certain fragrance components must be listed on the packaging of detergents if they are present at > 0.01 wt%. The component is listed using its INCI name, which can be confusing if the name required by the CLP Regulation is different.

These components of essential oils that require listing are the ‘fragrance allergens’ identified in Annex III of the Cosmetics Regulation (see below).

Cosmetics

Cosmetic products are applied to the skin or other body parts. The labelling of cosmetic products is given in the Cosmetics Regulation (1223/2009) [7]. The labelling of cosmetics does not follow the same rules as given in the CLP Regulation for general chemical products.

An ingredient list should be given on the cosmetic product label, giving the ingredients in descending order of concentration.

Fragrancing agents should be identified in an ingredients list as ‘parfum’ or ‘aroma’. Additionally, certain fragrance components must be listed on the packaging of detergents if they are present above certain thresholds, generally > 0.01 for rinse-off products and 0.001 wt% for leave on products.

These components of essential oils that require listing are the ‘fragrance allergens’ listed in Annex III of the Cosmetics Regulation.

Safety data sheets (SDSs)

The format and content of SDSs are detailed in the REACH Regulation.

A detailed guide to the content of SDSs in given in our resources page, or see our SDS services.

SDSs have slightly different formats for substances and mixtures.

As noted previously, essential oils can be regarded as substances, even though they are comprised of a complex mixture of components.

For essential oils as neat substances, the requirements are the same as for other chemical products. For reporting the contents of the substance in Section 3 of the SDS, the compiler can simply give the name of the essential oil, its EC number, and concentration (often 100%).

However, it is also common practice for the supplier to list the essential oil components and give their percentage in the essential oil. This is helpful to the recipient, as they can make better calculations concerning the classification of mixtures containing the essential oil (see above).

The component identities are also necessary for the labelling of cosmetic or detergent products.

For mixtures containing essential oils, particularly if more than one essential oil is present, it is helpful if the supplier gives the essential components in Section 3 of the SDS, rather than only naming the essential oils, although this latter option is legally allowed.

References

[back to What are essential oils] [back to Names and identification numbers] [back to Biocides] [back to Detergents] [back to Cosmetics]

[1] Essential oils: Guidance on Essential Oils in Cosmetic Products; Consumer Health Protection Committee (CD-P-SC); 2016.

[2] Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (as amended).

[3] Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures (as amended).

[4] Commission Decision (EU) 2019/701 of 5 April 2019 establishing a glossary of common ingredient names for use in the labelling of cosmetic products.

[5] Regulation (EU) No. 528/2012 of the European Parliament and of the Council of 22 May 2012 Concerning the Making Available on the Market and Use of Biocidal Products (as amended).

[6] Regulation (EC) No. 648/2004 of the European Parliament and of the Council of 31 March 2004 on Detergents (as amended).

[7] Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on Cosmetic Products (as amended).