What are essential oils? How do they affect us and where are they applied?

A healthy person breathes in & out approximately 23,000 times every day. Among other things mixed with the air, our respiratory system also receives fragrances.The sense of smell enables us to interpret and read out our environment.

Published: 28-09-2022

Scents can also recall our memories from the past or even the positive or negative emotions related to them.  Thus, fragrances accompany us for our entire lives. Whether those most beautiful or the ones less pleasurable, they all affect our feelings, living comfort and even our day-to-day decisions.

Why do we feel scents?

Smell is the most sensitive human sense. It allows humans to receive scents that they can record even unconsciously.  Scents can affect people’s behaviour as well as physical and mental state. This is mentioned in Egyptian papyruses and Hindu texts from ancient times and in the Bible and the Quran. The many written observations regarding scents show how important their role has been over the years.

Scents are sensed by breathing in the air that contains one or more fragrances. To detect a scent, its content  in the air must be higher than its minimum concentration.

In addition, the element or chemical compound will give off a fragrance if it shows a specific volatility and a high vapour pressure. It should also feature the capacity to penetrate the mucosa, our olfactory (‘smelling’) organ, and to form special complexes linked with receptor proteins located in the membrane of the epithelium’s receptor cells. These cells convey the information about receiving a stimulus to the rhinencephalon and further to higher structures of the central nervous system.

So what is a smell?

Smell (Latin: Olfactus) is the ability of elements, chemical compounds and their mixtures (odorants) to stimulate the smell organ through stimuli that cause specific behaviours.

In other words, a smell is the sense-perception of an odour (a smell) that registers in our brain as a result of the action of a chemical stimulus.

We often identify the term‘scent’ with ‘a nice fragrance’ (of essential oils, for example). However, ’scent” can in some cases refer to an unpleasant or neutral aroma.

In addition to the human ability to feel specific aromas, smells can have a therapeutic effect that supports good health. The field of natural medicine that uses the therapeutic effect of plants is called aromatherapy.

The key role is played here by essential oils, which contain active substances originating from flowers, leaves, roots, seeds or bark. These oils are used in the form of inhalants or as preparations applied on the skin during a massage, added to water in a bath, or are utilised in other cosmetic treatments.

How many olfactory stimuli can humans distinguish?

According to scientists, humans can differentiate several million colours and nearly half a million different tones, but the number of distinguishable smells has not been thoroughly tested. According to the available literature, humans can differentiate around 10,000 smells. However, this has never been confirmed empirically.

together with a team of other scientists, C. Bushdid has carried out psycho-physical tests aimed at determining the range and sensitivity of the human ability to smell.. He tested people’s ability to distinguish scent mixtures with different numbers of common ingredients. The results were spectacular, as they have shown that people can distinguish at least 1 trillion smells, much more than previous estimates. The conclusion is that the human smell system, with hundreds of different smelling receptors, exceeds by far other senses in terms of the number of physically different stimuli that can be differentiated.

What are essential oils and what do we use them for?

Often referred to as ‘liquid gold’, essential oils are a group of chemical compounds that are the source of specific intense smells. These substances are used to make various types of products such as:

  • perfumes, Eau de Toilette, deodorants;
  • white and coloured cosmetics;
  • cosmetics classified as personal hygiene products;
  • cosmetics and car accessories;
  • air fresheners;
  • detergents;
  • scented candles;
  • flavours and food products;
  • pharmaceuticals;
  • feeds and animal products;
  • agricultural preparations.

Essential oils are fragrant mixtures of organic chemical compounds. They exist in the form of an oily, often colourless liquid. Depending on the type and origin, they can be green, blue or brown. They feature a lower density compared to water. This is why they virtually do not dissolve in it. By contrast, their solubility is very high in such substances as ethyl alcohol, ether, chloroform, waxes and fats, vegetable and mineral oils and other etheric compounds.

Essential oils are formed as strongly concentrated extracts derived from various parts of plants (seeds, flowers, stems, leaves, roots). Their processing results in the formation of highly aromatic volatile substances. Aside from their aromatic qualities, the scent molecules originating from plants take part in many biochemical processes as particles used for transport and regulation. Another role is to protect against pests and pathogens. We cannot overestimate their contribution to the process of pollinating flowers by insects.

The content of aromatic substances in plants changes based on many different external factors. Their content can change even within one day.

Methods of producing essential oils

The source of essential oils are virtually all plants that exist in nature. However, only some of them contain a high number of aromatic compounds. This is why they are called oil plants. They generally belong to such families as Umbelliferae, Pinaceae, Labiatae, Rosaceae and Rutaceae.

Depending on the type of raw material, particular types of essential oils are extracted with various methods and processes. The most important of them are described below. We should know that the method of production directly affects the final properties of the oil.


Distillation is one of the most common methods of producing essential oils on a large scale. To put it in simple terms, distillation consists in converting a liquid into a vapour and then condensing it.

The distillation process can be carried out with the following three methods:

Steam distillation, which involves the boiling of water and then the permeation of the produced steam through plant parts and flower petals. At the next stage, the steam along with the volatile aromatic molecules is subjected to condensation. Then the water-insoluble essential oils separate from the condensed water.

The steam distillation method is used to produce essential oils from flower petals, leaves and stems of such plants that are highly resistant to high temperatures.

Dry distillation is a similar process but without steam. It consists in heating the raw material from which the essential oil is to be separated, which allows for acquiring diverse aromatic tones.

Fractioning is an additional stage of the distillation process. It consists in separating the ingredients of the mixture, where a particular amount of it is divided into smaller fractions. Then it is given specific properties according to particular instructions. This method allows the isolation of specified aromatic molecules that affect the modified features of an essential oil.


Extrusion is a method used to produce essential oils from citrus fruit peels. The oils are isolated by hand or mechanically using special presses. The citrus fruit are subjected to centrifugation or cold extrusion. In this way, we acquire highly aromatic bergamot, lemon or orange oils.

Extraction with organic solvents

Extraction is a method that uses various chemical compounds from the group of organic solvents. In this method, the solvents chemically bind a given essential oil originating from plant material submerged in a chemical substance.

The next year, the oil separates from the solvent. However, this implies the risk that a certain amount of solvent remains in the essential oil. This is why the oils produced by extraction are not used in aromatherapy. Such oils are mainly dedicated to perfume production.

Enfleurage: absorption

The enfleurage method, based on the process of absorption, is a quite complex, rarely used method of acquiring fragrances. It allows us to produce essential oils from flower petals.

The method consists in applying fat on special plates where flower petals are placed. The fat dissolves and binds the essential oils contained in the flowers. The next stage is to isolate the oil from the fat. This is possible thanks to alcohol.


Maceration is similar to absorption.  However, it requires the use of high temperature. Plant material is wetted in tanks filled with fluid fat. The tanks are put into a water bath heated to 50–70 °C. The process should take two days.

This way we obtain the product called concrete. It is dissolved in alcohol, which acts as a medium of aromatic compounds.

In industrial production, the flower-fat mixture is complemented by chemical compounds that dissolve unnecessary plant molecules. Their role is also to prevent the semi-finished product from breaking down, and preserves the final liquid’s clarity.

As we can see, the methods of producing the oils vary and depend on plant material, production scale and intended use. We should note that essential oils may penetrate into the human body when inhaled or absorbed through the skin. They have healing and relaxing properties, but we should not overuse them. Essential oils used in excess may irritate the skin or cause the body to react in other undesirable ways.

Standard groups of essential oils by extraction method

The selection of extraction method is very important in terms of the effect and intended use of essential substances. In consequence, we distinguish the following groups based on the oils that are produced:

  • monoterpenes – highly concentrated compounds characterised by antiseptic, anti-virus and bactericidal effects. Their improper use may lead to serious skin irritation. The most popular fragrance containing these compounds is pine oil.
  • esters – they give a very nice scent to essential oils. They have a soothing and relaxing effect. They also act as fungicides. The most important oils produced with the use of esters include bergamot, lavender and sage oils.
  • aldehydes – substances that feature an excellent antiseptic and relaxing effect. The group of oils produced with their use includes citronella oil and lemon balm oil.
  • ketones – compounds that stimulate skin hyperaemia. This group may also contain toxic substances. Examples of commonly used aromatic oils based on ketones include hyssop, sage and dill oils.
  • alcohols – are compounds with excellent antibacterial and antivirus properties. Typical substances containing alcohols include rose and geranium oils.
  • phenols – substances with a strong bactericidal and at the same time irritating The use of these compounds requires caution. They are used to produce the thyme, oregano and clove oils.
  • oxides – compounds with an expectorant and bactericidal effect. When contained in a fragrance, they show excellent effects in the treatment of respiratory diseases. The oils produced from them include the rosemary oil and the oil derived from the tea tree.

We should note that essential oils are highly sensitive to UV radiation and to low and high temperatures. These substances often easily dissolve in alcohols and oils. They sparingly dissolve in water, forming short-term suspensions.

The high quality of oils is determined mainly by the quality of plant material. Therefore, we should take care that it comes from ecological and sustainable sources.

Application and effect of essential oils

Essential oils play a very important role in the cosmetic industry, owing not only to their aromatic qualities but also due to the ability to penetrate through the skin. These compounds, with their properties, have various effects on human body. They effectively strengthen the skin and can act as relaxants or stimulants.

The use of essential oils in cosmetics cannot be overestimated.  They are applied in aromatherapy as appropriately formulated aromatic mixtures. The oils soak into cosmetic scent tissues, but most of all they are used for the production of perfumes, deodorants, creams, balsams, and personal hygiene products such as soaps, shampoos, shower gels or hairdressing agents.

Essential oils also have an excellent aromatherapeutic effect. They are excellent for use during spa and wellness treatment (massages, masks, cosmetic treatments, inhalations, compresses, saunas).

Essential oils:

  • improve skin condition: they brighten, smooth and improve the texture of the skin;
  • soothe and reduce allergies and skin diseases (pannus, mycosis, eczemas);
  • heal burns;
  • accelerate the healing of wounds;
  • stimulate the skin (remove toxins, peel off epidermis);
  • have a relaxing and soothing effect from being smelled.

High-quality essential oils are an amazing treasury of valuable ingredients of vegetable origin. They are used not only in cosmetics but also in the production of candles, food products, textiles, detergents, animal feeds, drugs and many other products. 

Example effects of essential oils used in cosmetics

The principal asset of essential oils is their scent. But is this the most important feature? Of course, the aromatic compounds give a specific scent to products, but they can also play an important therapeutic role in treating various diseases. Below we give a few examples:

  • patchouli oil prevents skin ageing under the influence of UV radiation;
  • tea tree, lavender or copaiba oil treats acne and prevents the formation of skin lesions;
  • mirra oil has a soothing effect on sensitive skin;
  • sandalwood oil prevents the formation of wrinkles, smooths the skin, improves its texture and prevents the formation of changes on the skin;
  • lavender oil makes the skin more flexible, smooths it, improves its texture, has a soothing and relaxing effect, and alleviates and reduces skin lesions;
  • rosemary, mint and clove oils support the growth of hair and makes it softer and more elastic.

The above examples are only a few items from the long list of beneficial properties of essential oils. However, the aromatic and therapeutic qualities should not confuse the issue of safety of their use. The key problem here is the choice of optimum concentrations of the aromatic compounds. They should be selected and administered with care, as some of them may be allergenic or phototoxic.

Safe use of essential oils in cosmetics

Despite the natural origin of essential oils, they should be used with caution. It is a specific group of cosmetic ingredients which, at high concentration, may be toxic, photosensitising or allergenic.

In the cosmetics and perfume production industries, there are so-called dermal limits, which are available on the website of the International Fragrance Association (IFRA). The objective of the association is to promote and ensure the safe use of fragrances in cosmetics, detergents, hygienic articles, toys and many other products of daily use.

The IFRA publishes a collection of standards that regulate the use of fragrances. Their safety is assessed in the first instance by the Research Institute for Fragrance Materials (RIFM). The team of experts from the RIFM consists of high-level specialists in dermatology, pathology and toxicology as well as scientists and practitioners in the field of environmental protection. The IFRA members are required to comply with the standards and the RIFM Code of Conduct, which contain the rules of the production and handling of fragrances. We should know that 90% of fragrance producers operating worldwide are members of the IFRA.

In addition to the standards and guidelines of the IFRA, the provisions on the production and use of aromatic compounds are regulated by the European Union, which has defined them in various publications. The most important one is ‘Essential Oils Safety’ by Tisserand and Young.

What are dermal limits and why are they so important?

Dermal limits are the maximum allowable doses of a substance that ensure the safety of its use by people.  Owing to dermal limits, only such products are admitted to sales that show specific concentrations of chemical compounds, which in doses higher than recommended may cause irritations, allergic reactions and other health issues. The limits also apply to essential oils, which contain compounds considered to be detrimental to health (toxic, phototoxic, carcinogenic substances, etc.).

Cosmetic producers offering their products in the EU and in countries that respect its directives (Brazil, China) are required to strictly observe the regulations concerning dermal limits.

Obligations of cosmetics producers

In accordance with the EU Cosmetics Regulation 1223/2009, cosmetics producers must show on the labels the names of any allergising fragrances contained in the product. Currently there are 26 registered substances which must be indicated if their content in a cosmetic exceeds 0.001% for a product remaining on the skin or 0.01% for a washable product.

Presently there are around 3,000 fragrances available on the market. They are used in cosmetic products, detergents, cleaning agents, air fresheners, hygienic products, and toys. Common use of fragrances increases human exposure to their effects. In consequence, there is a growing risk of allergic reactions and skin irritation.

How to safely use essential oils?

It is commonly known that ‘the dose makes the poison’.  Therefore, the core principle in the use of essential oils is moderation. Aromatic compounds used at appropriate concentrations are safe and have therapeutic and healthy effects. However, we should remember that the overuse of highly concentrated extracts may cause the formation of an allergy or other skin-related problems.

In order to safely use essential oils, we must observe the following rules:

  • essential oils are not suitable for consumption. If administered orally, they can cause burns of the oral cavity, tongue, oesophagus and internal organs;
  • do not apply a concentrated essential oil directly on skin. Before use, it is required to dilute the essential concentrate in the base oil;
  • essential oils must be kept away from children;
  • the oils should preferably be stored in tight glass vessels with a dark colour, away from sunlight;
  • essential oils contained in each cosmetic must be appropriately diluted. This also applies to cosmetics produced in household conditions for one’s own use. Essential compounds are substances that do not dissolve in water, vinegar, 40% alcohol, or glycerine. They do dissolve in substances such as spirit or perfume alcohol, fats, some cosmetic emulsions, solubilisers (mists, spays, micellar solutions), and surfactants (soaps, shampoos, gels).

List of allergising fragrances

The following 26 fragrances are considered by the EU to be allergising compounds, according to the INCI names:

  1. Amyl cinnamal,
  2. Benzyl alcohol,
  3. Cinnamyl alcohol,
  4. Citral,
  5. Eugenol,
  6. Hydroxycitronellal,
  7. Isoeugenol,
  8. Amylcinnamyl alcohol,
  9. Benzyl salicylate,
  10. Cinnamal,
  11. Coumarin,
  12. Geraniol,
  13. Hydroxyisohexyl 3-cyclohexene carboxaldehyde,
  14. Anise alcohol,
  15. Benzyl cinnamate,
  16. Farnesol,
  17. Butylphenyl methylpropional,
  18. Linalool,
  19. Benzyl benzoate,
  20. Citronellol,
  21. Hexyl cinnamal,
  22. Limonene,
  23. Methyl 2-octynoate,
  24. alpha-Isomethyl ionone,
  25. Evernia prunastri ex­tract,
  26. Evernia furfuracea extract.

It is quite probable that the above list will eventually include other fragrances whose safety is monitored by the EU’s Scientific Committee on Consumer Safety.

Essential oils prohibited in the EU

In addition to the IFRA guidelines, cosmetic producers are required to control the composition according to Regulation (EC) No. 1223/2009 of the European Parliament and of the Council on cosmetics products. The regulation prohibits the use of specified essential oils and other substances derived from aromatic plants.

These include, without limitation:

  • Ammi majus L. and its galenical preparations (including essential oil);
  • Apocynum cannabinum L. and its derivatives;
  • Chenopodium ambrosioides L. (essential oil);
  • Anamirta cocculus L. (fruit products);
  • pecacuanha (Cephaelis ipecacuanha Brot.) and related species (roots, powder and their products);
  • Lobelia inflata L. and its preparations;
  • Prunus laurocerasus L. (‘cherry laurel water’) and its derivatives;
  • Juniperus sabina L. (leaves, extract and other preparations);
  • Schoenocaulon officinale Lind (seeds and preparations);
  • Pyrethrum album L. (raw material and preparations);
  • Laurus nobilis L. (seed oil);
  • Alanroot oil (Inula helenium L.) (products);
  • Ficus carica L. (leaf absolute);
  • Lippia citriodora Kunth. (products other than absolute);
  • Saussurea lappa Clarke (oil).

Apart from the mentioned items, restrictive limitations also apply to other essential oils and plant extracts. The following guidelines can be an example:

  • extracts and essential oils acquired from plants such as silver fir, Siberian fir, white fir, balsam fir, bog pine, Scots pine, black pine, longleaf pine, maritime pine, Swiss pine and other pines, black spruce, northern white-cedar, Atlas cedar, Mediterranean cypress and turpentine must show a peroxide index of below 10 mmol/l.
  • the admissible level of extracts and distillates of the balsam of Peru is 4%;
  • the admissible level of oil and extracts of cumin in leave-on products is 4%;
  • the oil and extracts of benzoin (Liquidambar orientalis and Liquidambrar styraciflua) may not be used at a dose exceeding 6%;
  • the oil and extracts of the opoponax resin may not be used at a dose exceeding 6%;
  • the opoponax chironium resin may not be used at a concentration exceeding 6%;
  • the absolute of the Lippia citriodora Kunth. may not be used at a concentration exceeding 2%.

The topic of essential oils is quite extensive. Generally,  they are substances with a highly complex chemical composition. Although they are a great boon of the nature, they can have adverse effects if used in excess. However, if we use them with care, their properties can be of great benefit. There is a reason why people have used essential oils for over 5,000 years. Egyptian and Greek women would use them as aphrodisiacs. What is more, these compounds were used in ancient Egypt to embalm bodies of the deceased.

Today, essential oils are again enjoying a renaissance. Their magic power will be appreciated by anyone who experiences their soothing effect at least once.



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