Essential oils and safety assessment

Essential oils have become an integral part of everyday life. They are used in many ways - from flavouring agents to the essence of cosmetic products. When using essential oils in cosmetics, it is important to pay attention not only to the desired properties of the oil in question, but also to the safety of their use. Many people consider natural essential oils to be completely safe. This is due to the misconception that all herbs are safe because they are natural. The toxicity of essential oils can also be quite different from herbs, not only because of their high concentration, but also because of their physicochemical properties. Essential oils are mixtures of mainly low-molecular-weight chemicals, which, combined with their lipophilicity, results in their ability to be absorbed very efficiently through the skin.

What exactly are essential oils?

The most developed definition of an essential oil in terms of its use in public health can be found in the European Pharmacopoeia. According to it, an essential oil is: "an aromatic product, usually of complex composition, obtained from a botanically defined plant material by steam distillation, dry distillation or a suitable mechanical process without heating. Essential oils are usually separated from the aqueous phase by a physical process that does not significantly affect their composition."

Methods for obtaining oils

The choice of essential oil extraction method depends on the original state and properties of the plant material. The extraction method determines the characteristics of the essential oil such as viscosity, colour, solubility, volatility and can result in enrichment or depletion of certain components. Three main extraction methods are used:

-Vapour distillation - essential oils are produced by passing steam through the plant material in a suitable apparatus. The steam and oil vapours are condensed. The water and essential oil are then separated by decantation.

- Dry distillation - essential oil is produced by high-temperature heating of the stems or bark in a suitable apparatus without the addition of water or steam.

- Mechanical process - essential oil is produced by a mechanical process without heating, usually called 'cold pressing'. It is mainly used for citrus fruits and involves squeezing the oil from the pericarp and then separating it using physical methods.

Physicochemical nature of the oils

Essential oils are usually volatile substances that are liquid at room temperature; this distinguishes them from so-called solid oils. They are slightly coloured and their density is generally lower than that of water. They have a high refractive index and mostly turn polarised light. They are soluble in lipids and common organic solvents while they are very poorly soluble in water. Essential oils are complex mixtures of various components in varying concentrations. These components mainly belong to two groups characterised by different biogenetic origins: terpenoids and substances biosynthesised from shikimic acid, giving rise to phenylpropane derivatives. The analysis of essential oils aims to identify each of the components, can be carried out using techniques such as gas chromatography on polar, apolar or chiral stationary phases and can be combined with mass spectrometry or Fourier transform infrared (FTIR) detection.

Quality of essential oils

The safe use of essential oils in cosmetic products depends on both the quality of the raw materials used and the extraction method by which the pure essential oil is produced. Essential oils should have identified specific physical and chemical characteristics and be stored in well-filled, airtight containers protected from light. The physical, organoleptic, chemical and chromatographic properties of essential oils are established globally through various ISO standards. There are also ISO standards relating to nomenclature and general rules for packaging, packaging and storage of essential oils. The identity of the initial plant material is required to ensure traceability through to use in cosmetic products. This issue can be addressed by providing certificates (where applicable) or documented supplier declarations.

Potential toxicity of essential oils

Many essential oils that are considered non-toxic can have harmful effects on certain groups of people. These effects may be influenced by a previous allergy to a particular essential oil, a group of essential oils containing similar ingredients or an ingredient in an essential oil. A person's age is also important, so the very young and the elderly are particularly vulnerable to products applied to the skin. With this in mind, care should be taken when using essential oils in topical cosmetic products.

Regulations

In the European Union, cosmetic products are regulated by the Cosmetics Regulation (EC) No 1223/2009, for which certain provisions relate specifically to the use of essential oils in cosmetic products, primarily in Annex II and Annex III. It is incumbent on the responsible person to ensure that the products they place on the market comply with these regulatory requirements. The Cosmetics Regulation imposes an obligation on responsible persons to ensure that a cosmetic product has undergone a safety assessment on the basis of appropriate information before it is placed on the market. Annex II of Regulation (EC) No 1223/2009, as amended, lists substances that are prohibited for use in cosmetic products. Among the substances listed in this Annex are:

-plant ingredients that are prohibited in cosmetic products, regardless of function;

- plants and their compounds that are prohibited in cosmetic products with a specific function (perfume ingredients);

-substances that are prohibited in cosmetic products unless they are naturally present in the extracts, and essential oils that are subject to concentration limits.

In general, the unintentional presence of a small amount of a prohibited substance from, for example, natural ingredients is acceptable where it is technically unavoidable as part of good manufacturing practice, provided that such presence is safe (Article 17 of Regulation 1223/2009/EC).

Annex III to Regulation (EC) No 1223/2009 contains a list of substances that may be included in cosmetic products only subject to certain restrictions. This annex includes, among others, 26 substances, known as fragrance allergens, subject to mandatory labelling conditions due to their allergenic potential. There is now a draft regulation increasing this number of allergens to 62. Their presence in cosmetic products must be mentioned on the packaging when their concentration exceeds the threshold of 10 ppm (0.001 %) in leave-on products and 100 ppm (0.01 %) in rinse-off products. The Council of Europe has published three volumes of recommendations on the use of plants and plant preparations used as ingredients in cosmetic products. They are in addition to the publication on the safety testing of ingredients used in cosmetic products and the recommendation to avoid the use of camphor, eucalyptol or menthol in cosmetic products for infants. The entries are divided into three categories: plants that do not pose a health risk; plants for which further information is needed; and plants that may pose a health risk and are not recommended for use in cosmetic products. Despite the long history of the use of natural raw materials, such as plants and plant preparations, in cosmetic products, the Council of Europe's Committee of Experts on Cosmetic Products has noted that some raw materials contain substances with significant activity that could be potentially harmful to consumers. Therefore, when assessing the overall safety of a cosmetic product, it is necessary to take into account the risk that these substances may pose to consumers.

Recommendations of the International Fragrance Association (IFRA)

The IFRA Scientific Committee collects and makes available data on the safety assessment of fragrance ingredients. As many fragrances contain essential oils and their constituents, this information should be taken into account by those developing cosmetic formulations with essential oils. IFRA issues standards for fragrances, the safety of which is first assessed by the Research Institute for Fragrance Materials (RIFM). The RIFM Expert Panel is made up of dermatologists, pathologists, toxicologists and environmental scientists. All IFRA members are required to adhere to the IFRA Code of Practice, which aims to provide recommendations for good operational practice and guidelines for assessing the safety of fragrance ingredients, and includes fragrance safety standards that may restrict or prohibit the use of certain fragrance materials. The organisation's mission is to ensure the safety of fragrances in a variety of products - from cosmetics to household chemicals to toys and hygiene products. It is thanks to IFRA that a list of 26 fragrance allergens has been created.

Risk assessment of essential oils in cosmetic products

Essential oils are very interesting natural plant products with various biological properties. Given that essential oils are mixtures of volatile organic substances of known chemical structure that react, either singly or in combination to produce biological responses, it should be possible to relate ingested doses of these substances to observed toxicity. It is often assumed that essential oils are not hazardous because they are derived from plant materials. However, some essential oils may cause skin reactions or irritate the eyes and mucous membranes in a dose-dependent manner. Symptoms may persist for several days after skin contact with the product. Some oils used in deodorant sprays can also promote asthmatic attacks. There are also some that cause phototoxic effects on the skin after application. Due to the complexity of these natural products, toxicological and biochemical studies of an essential oil should take into account the totality of its constituents, which may act with each other in an additive, synergistic or antagonistic manner. Essentially, it is the interaction between one or more of the molecules in an essential oil and the macromolecules that causes a biological response, whether it is a desired functional effect, such as a pleasant fragrance, or a potential toxic effect. The chemical composition of an essential oil is fundamental to understanding the factors affecting its safety in a cosmetic product. The risk assessment associated with the use of essential oil as an ingredient in cosmetic products must follow the cosmetic product assessment process recommended by the SCCS in addition to the legal basis for the safety assessment of a cosmetic product according to Annex I of Regulation 1223/2009/EC. However, due to the complex nature of essential oils, which usually consist of mixtures of many substances, appropriate supporting or alternative methodologies may be needed. According to the cosmetic product guidelines, the assessment of essential oils by a safety assessor may include:

- an analytical phase in which the quantitative composition of the essential oil is determined as comprehensively as possible by using suitably validated analytical methods;

- an extensive literature search on the essential oil and its chemical constituents identified during the analytical phase,

- the hazard characteristics of these chemicals individually and, if possible, of the essential oil mixture under consideration,

- exposure assessment under conditions of use (including dermal exposure and, due to volatile properties, inhalation),

- a risk assessment using all the information obtained.

The risk assessment of a cosmetic product containing essential oils is based on exposure to the essential oils concerned or their constituents. Exposure data will be determined on a case-by-case basis depending on the use of the product. The following parameters should be taken into account:

- type of cosmetic product;

- concentration of the substance in the finished cosmetic product

- the amount of product used for each application;

- frequency, duration, area and place of application;

- target population;

- normal and reasonably foreseeable conditions of use;

- exposure area.

It is necessary to refer to the SCCS guidelines, which indicate the average surface area per type of cosmetic product, as well as the daily exposure to cosmetic products. For the toxicological profile of essential oils, skin sensitisation is an important element. Not only the dose per unit area of allergen, but also the number of exposures, i.e. the cumulative dose, is relevant for the risk of contact allergy induction. The induction of contact allergy is an immunological process, taking place without clinical symptoms. If exposure is continued or re-exposed with an adequate dose of allergen, the induction phenomenon occurs. This is an inflammatory reaction (eczema) with clinical signs in the form of erythema, thickening and, in some cases, vesicles. Characterisation of intrinsic hazards and risk assessment under conditions of reasonably foreseen use requires a sequential approach, based first on literature data on the essential oil in question and its chemical constituents. In the absence of data, toxicological studies should be used to identify and characterise the hazard of the essential oil. Based on the data (hazard and exposure) examined by the safety assessor, the conclusion of the expert opinion must answer the following questions:

- Can an essential oil be used in a cosmetic product to be considered safe for the consumer?

- Are essential oils subject to restrictive conditions of use in a cosmetic product?

- Do essential oils require special conditions of use in a cosmetic product?

The elements and procedures used to assess risk must be clearly described and the reasoning that led to the conclusion must be clearly justified.

Summary

Essential oils have been used in cosmetic products for centuries. This history of use may be a reassuring factor to consider. However, it is important to note that some of these oils may be harmful to consumers when added to cosmetic products due to their absorption through the skin or inhalation. Although essential oils are usually used in diluted form in cosmetic products, this is not always the case. If products containing high concentrations of essential oils are used inappropriately, the effects can be harmful, especially in sensitive people such as those with allergies and children. This is why it is so important to have a thorough safety assessment of the essential oil used in the finished product by a qualified safety assessor supported by sound evidence and concluded with the issuing of a safety assessment report.

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