Essential oils are complex mixtures of organic substances of various chemical nature, obtained by extraction starting from plant material rich in essences; they are present, albeit in different quantities, in almost all plants, but are more contained in those belonging to the Labiate family, also called aromatic plants or essential plants.
Essence and essential oil cannot be considered synonyms as the term essence refers to the set of various chemical constituents present within the plant (in the organs of synthesis, collection and secretion); essential oils instead consist of the same group of substances once extracted from the plant and others formed during the various stages of the extraction process.
Although they are called oils, their molecular structure and texture are very different from vegetable oils; once extracted they appear as oily, liquid, very volatile substances, generally liquid at room temperature, colorless or pale yellow or orange (but they take on a green-blue / blue color if they contain azulenic compounds, eg Matricaria chamomile). They have a high boiling point (150-300 ° C), insoluble or slightly soluble in water, soluble in fats and in organic solvents such as alcohol, ether, chloroform, ethyl acetate. The taste (acrid-spicy) and the smell are related to the chemical content.
Essential oils represent the most regal part of the plant, they are produced in the cytoplasm by specialized cells associated with the secretory organs (glandular hairs, secretory pockets, secretory channels) and are collected inside the plant cells in the form of tiny droplets inside rounded cavities called vacuoles. They can be found in different structures of the plant (flowers, leaves, fruits, bark, wood, branches, stems, roots and rhizomes, buds, resin) to which they give the characteristic odor.
For some varieties of plants it is possible to extract different essential oils from a quantitative and qualitative point of view using different parts of the same plant: an example is Citrus aurantium, the bitter orange plant, from which three different essential oils can be extracted using as extraction material, the rind of the fruit (essential oil of bitter orange), the flowers (essential oil of neroli) or the leaves and twigs (essential oil of Petitgrain); moreover, essential oils coming from the same organs of the same variety of a plant can still differ in yield and quality (fragrance, color, density and viscosity), as these factors are closely related to variables such as cultivation soil, climatic and nutritional conditions, moment of collection, type of extraction. The chemical composition can also vary significantly: sometimes populations of plants of the same botanical species but grown in different places in terms of altitude, latitude and soil characteristics, can produce essential oils with different chemical compositions; in these cases we will talk about chemotype (= chemical type).
Essential oils are intimately connected to the vital processes that take place in the plant organism: they are formed in the green parts in response to pathological processes or as by-products of metabolism; as the fabric ages, they migrate to other fabrics, mainly in the flowering branches, where they can change by oxidation, esterification, etc. Like many other secondary products, they have long been considered waste products; however the biosynthetic pathways that lead to their formation are highly specialized and their production involves a considerable energy expenditure by the plant; this led to the formulation of various hypotheses on their function in the physiology of the plant including those of:
- attract pollinating insects: thanks to the high volatility and aroma that simulates that of the sex hormones secreted by insects, mammals and birds;
- contribute to the conservation of the species: with the rain, essential oils are deposited and penetrate the soil, preventing different plants from germinating;
- prevent dehydration in very dry environments: essential oils surround the parts of the plant with a halo of steam, preventing the loss of too much water;
- giving an unpleasant taste to the plant as a defense against herbivorous animals;
- perform a nutritional function: placing a plant in the dark, it completely loses the odorous principles that would seem to be used as nutritional elements to replace the metabolites normally synthesized during photosynthesis;
- defend against parasites and protect against bacterial and fungal infections;
- promote the healing of damaged plant tissues;
- act as moderators of cellular oxidative processes.
The essential oil content within the aromatic plant represents only a minority percentage, on average between 0.01 and 2%, for which 100g to 2Kg of essential oil can be extracted from 100kg of plant (depending on the type of plant and the type of extraction). For the extraction of the essential oil, the plants are generally used fresh and, as soon as possible, subjected to the necessary treatments to avoid any fermentation. The dry plant is typically used for imported drugs. The hard parts of the plant (wood, bark, root, rhizome, seeds) are cleaned and crushed before being subjected to the extraction process.
Enfleurage: very ancient method, now almost completely fallen into disuse, used to extract essential oils from petals and very tender and delicate parts of plants, which would be easily damaged if subjected to the heat of distillation. The flowers are placed on plates covered with purified fat, exploiting the ability of the fat to absorb odors. The flowers give their perfume to the grease and are replaced with other flowers, until the grease is saturated with perfume. Then the fat is dissolved with alcohol and then the essential oil is separated.
Squeezing: this technique is reserved for those essential oils contained in large quantities in the peel of fruits of the genus Citrus (lemon, orange, grapefruit, mandarin). It is a mechanical extraction process that is carried out cold and does not include any chemical treatment. The rind of the fruit is chopped and subjected to pressure in special hydraulic presses with the addition of a little water; the mixture of oil and water is then separated with a centrifuge.
Solvent extraction: this type of extraction is suitable for extracting delicate flowers, such as rose and jasmine, containing essences that would alter if subjected to heat. The drug is passed through by a suitable solvent (ether, benzene, hexane ...) which allows its extraction but at the same time is not toxic or has a bad smell. The solvent is then removed from the obtained oil.
Steam distillation: it is a separation process based on the fact that some of the components present in a plant matrix evaporate more than others. This technique exploits the phenomenon according to which the boiling temperature of a mixture consisting of two immiscible liquids (essential oil and water) is lower than the boiling temperature of the most volatile component (essential oil): according to this principle, essential oils (thermolabile compounds ) can be extracted without undergoing degradation, as the temperature reached during distillation never exceeds 100 ° C.
It is one of the most used methods for the extraction of essential oils and is carried out through the use of the distiller, an instrument made up of several watertight containers, a steam generator and a cooling coil. The steam current can invest the vegetable directly (distillation) or indirectly (hydridostillation).
In distillation, the steam is produced by a generator (boiler) and introduced into the distillation chamber (container in which the drug is placed). The steam comes into contact with the plant material, relaxes it, softens it, increases the permeability of its membranes until the cells themselves break, allowing the essence to escape and be transported according to the flow of the steam itself. This is then collected in a collector tube up to the cooling coil; here the vapors laden with essential oil condense and, since essential oil and water are immiscible from each other, they separate by stratifying: the essential oil, lighter, above water.
In hydrodistillation, on the other hand, the plant material is immersed in water which is heated to boiling, causing the formation of the steam flow which drags the essential oil into the condenser and then into the decanting system.
In both cases the water recovered in the decantation can be sent back to the still or recovered in a system where the separation of the two phases by gravity takes place, with the discharge of the aromatic water (or hydrolat) in the lower part of the system and collection of the essential oil from above.
Sometimes the essential oil obtained is subjected to further distillation or rectified in order to eliminate any non-volatile residues; moreover, some essential oils are distilled at different temperatures to obtain certain constituents and exclude others, in this case the essential oil can no longer be defined as integral or natural, but made functional for a specific application.
For essential oils intended for therapeutic use, the European and Italian Pharmacopoeias allow only two extraction procedures: steam distillation and cold pressing.
The chemical composition of essential oils is very complex: they are made up of a mixture of more than 200 compounds that can be distinguished in a volatile fraction which constitutes 90-95% of the total content and a non-volatile residue represented by the remaining 5-10%. In particular, the volatile fraction consists mainly of monoterpenes and sesquiterpenes and their oxygenated derivatives; the oxygenated fraction is the main responsible for the characteristic aroma of essential oils.
The chemical compounds that characterize them are formed by groups of hydrogen, carbon and oxygen and can be divided into two groups: unsaturated hydrocarbons (-CH-), consisting almost exclusively of terpenes, and oxygenated compounds (-CHO-), mainly esters , aldehydes, ketones, alcohols, phenols and oxides; sometimes there are also acids, phenylpropanoids (such as lactones, coumarins, furanocoumarins), nitrogen compounds and sulfur compounds.
- Terpenes (suffix –ene), synthesized starting from molecules of mevalonic acid, consist of isoprene polymers containing multiples of 5 carbon atoms and in particular: monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), triterpenes (C30 ) and tetraterpenes (C40). Monoterpenes and sesquiterpenes are the main components of essential oils, but they are also characterized by marked irritating properties on the mucous membranes because, not being oxygenated, they have greater affinity with the lipid components of the membranes and skin. Monoterpenes are very volatile and possess antiseptic and antibacterial properties; among the most common we find: pinene, fellandrene, terpinene, limonene, myrcene. Sesquiterpenes, on the other hand, are characterized by marked anti-inflammatory properties; among the most representative there are chamazulene, α-bisabolol, β-caryophyllene, β-farnesene, cardinene.
- Oxygenated compounds (-CHO-), mainly aldehydes, alcohols, ketones, phenols, esters and oxides, which consist of the oxygenated variant of terpenes (in particular mono and sesquiterpenes) with a functional group that confers particular properties to the compound:
- Alcohols (suffix –olo): monoterpenic compounds often endowed with low irritating power for skin and mucous membranes, while maintaining a moderate antibiotic, antiseptic and antiviral power; thanks to their structure, they make available their hydroxyl group which comes out of the cell membrane and interacts with proteins carrying out various functions: antiseptic, toning or calming on the nervous system, toning of smooth muscles. Thanks to the hydroxyl groups they are more soluble in water and for this reason they are found in a fairly high concentration in the distillation waters, to which they give a perfume similar to that of essential oil; the most common are borneol, thujanol, terpineol, linalool, geraniol, menthol, citronellol.
- Ketones (suffix –one): derive from the oxidation of alcohols, they are less irritating than aldehydes but if present in high quantities they can be neurotoxic; they possess mucolytic, healing and anti-inflammatory activity; among the most common we find menton, carvone and camphor.
Phenols (suffix –olo): compounds generally endowed with antibacterial, antifungal, antispasmodic activity; if present in high concentrations they can be irritating to skin and mucous membranes; the most common are thymol, carvacrol, eugenol.
- Foreign: they are obtained from the synthesis of a monoterpenic alcohol (suffix –yl) with an aliphatic acid (suffix –ate); they are generally fragrant and often have a fruity aroma; possess anti-inflammatory, revulsive, antispastic activity of smooth muscles; among the most common are the esters of linalool, geraniol and nerol (linalyl acetate, bornyl acetate, benzyl benzoate).
- Oxides: obtained by oxidation of monoterpenic hydrocarbons, they are formed by dehydration of two hydroxyl groups; act as powerful expectorants by stimulating the mucous glands of the respiratory tract; the most common is eucalyptol (1-8 cineole).
- Phenylpropanoids: they are synthesized in the plant starting from shikimic acid and include a heterogeneous group of compounds; among the most common in essential oils we find lactones, coumarins and furanocoumarins; the latter can cause photosensitivity (ex: bergapten contained in the essential oil of bergamot).
- Acids: very rare in essential oils, important because the important group of esters originates from them. Of the acids we find after distillation, many are probably artifacts due to the hydrolysis of esters; others instead, such as myristic acid, are present in the original aromatic material. More common examples are benzoic acid in benzoin and geranic acid in geranium.
- Sulfur compounds: very reactive chemical compounds found in rare essential oils, especially those contained in plants of the genus Allium (such as garlic and onion). They often have an unpleasant and very strong aroma, they can be irritating and sensitizing.
- Nitrogen compounds: they are contained in high concentrations for example in the essential oils of ylang ylang and jasmine and determine the floral aroma of these essences.
Essential oils have three distinct modes of action:
- Pharmacological effect: chemical changes that occur when an essential oil enters the circulation and reacts with hormones, enzymes, etc.
- Physiological effect: ways in which the essential oil affects the systems of the body, carrying out its action.
- Psychological effect: it is determined each time an essential oil is inhaled and the individual reacts to its smell.
The essential oil always works by combining two of its properties: high transcutaneous penetration power and high volatility. In this way its action is always the result of physical effects combined with psychological ones. To this must be added a high bactericidal and / or bacteriostatic capacity that is expressed both inside the body and on the skin. The application of essential oils for aromatherapy use concerns:
- Skin and its appendages: skin problems often represent the superficial manifestation of a deep pathological state (toxins, hormonal imbalance, nervous and emotional problems); essential oils are particularly suitable for this type of problem thanks to their versatility, or the ability to perform multiple actions:
- antiseptic; for cuts, insect bites, stains etc. (e.g. lavender, lemon, tea tree, eucalyptus, thyme, sage)
- anti-inflammatory; for eczema, wounds, bruises etc. (e.g. lavender, chamomile)
- fungicide (e.g. lavender, tea tree, patchouly)
- healing; for burns, cuts, scars, stretch marks (e.g. lavender, chamomile, neroli, geranium)
- deodorant; for excessive sweating (e.g. bergamot, lavender, juniper, cypress)
- parasiticide; for lice, fleas, mites, mosquitoes (e.g. lemongrass, lavender, geranium, eucalyptus)
- Circulation, muscles and joints: essential oils easily penetrate into the bloodstream through the skin and mucous membranes, influencing the general character of circulation: oils with rubefacient effects determine an improvement in circulation locally, produce a sensation of heat and hyperemia (redness) on the surface of the skin and can provide considerable relief of pain thanks to their analgesic and desensitizing action; they can also relieve local inflammation by releasing mediators in the body that can cause blood vessels to expand, so as to allow blood to circulate more quickly and reduce swelling. In these cases we will talk about essential oils with action:
- rubefacient; for joint rheumatism, muscle stiffness, etc. (eg juniper, rosemary, eucalyptus, lavender, peppermint) - lymphatic stimulant; for cellulite, water retention etc. (e.g. juniper, lemon, fennel, geranium, rosemary, orange)
- circulatory and astringent tonic (eg cypress, lemon, orange, rosemary, clary sage)
- Respiratory System: inhalation is a very effective method to exploit the properties of essential oils since, even if after reaching the bronchi most will be exhaled directly from the lungs, they still cause an increase in bronchial secretion (as a defense reaction) which it is beneficial for many respiratory ailments. Essential oils active on the respiratory system have an action:
- expectorant; for phlegm, sinusitis, cough etc. (e.g. eucalyptus, thyme, sandalwood, fennel)
- balsamic; for colds, congestions, colds, etc. (e.g. eucalyptus, peppermint, pine, lavender, thyme)
- antiseptic; for sore throat, cold, etc. (e.g. thyme, sage, eucalyptus, pine, tea tree)
- Digestive system: some essential oils can alleviate some disorders of the digestive system following external application, conveyed in a vegetable oil and massaged with circular movements on the abdomen; the main actions performed are of the antispasmodic and carminative type in case of pain, abdominal tension and dyspepsia. Examples of essential oils active in this are chamomile, fennel, lemon balm, clary sage, peppermint etc.
- Nervous system: each essential oil manages to bring its own beneficial effects on the nervous system through the smell it emanates, which influences the mood and psychological state of the subject. The nasal cavity, in fact, is rich in olfactory nerve endings, where the odorous stimulus is transformed into electrical impulses that stimulate the nervous system. However, terms such as "relaxing" and "exciting" have more to do with the description of odors and the emotional response than with the physiological effect, although the two are closely related. Essential oils active on the nervous system have properties:
- relaxing; for nervous tension, stress, insomnia etc. (e.g. chamomile, lavender, lemon balm, lemon, bergamot)
- stimulating; for nervous fatigue, asthenia etc. (e.g. peppermint, ylang yalng, neroli, rosemary)
- tonic; to strengthen the nervous system in general (e.g. chamomile, clary sage, lavender, rosemary)
Before using essential oils it is always advisable to consult the opinion of an aromatherapy expert, and in any case, some essential precautions must be taken such as: buying 100 pure essential oils%; check for any allergies if you are using an essential oil for the first time (apply a drop in the inner crease of the elbow and wait a few minutes to ensure that no redness and irritation occur) do not use them pure but always diluted in a vegetable oil and in low concentrations; do not apply them pure on the mucous membranes and avoid contact with the eyes; keep them in a cool place, in tightly closed dark glass jars to protect them from oxidative phenomena; keep them out of the reach of children.
Essential oils can be used in a simple and effective way in various ways that exploit their cosmetic and aromatherapy properties: localized or extended massages to the whole body; aromatic showers and baths; hand baths and foot baths; hair treatments; masks and applications on face and body.
- Massage: represents the most widespread form of treatment as it combines the beneficial effects of the movements of the massage on the part of the body treated with the specific therapeutic value of each essential oil used; moreover, the application on the skin through massage maneuvers facilitates the absorption and penetration of essences. It can be done locally or extended to the whole body. The content of essential oils to be conveyed in vegetable oil is generally between 1 and 3%, depending on the type of disorder. In general, 20 drops of essential oil are equivalent to one milliliter, so for 100ml base oil 20 to 60 drops will be added (3-5 drops for a tablespoon).
- Preparations for skin and hair care: a few drops of essential oil can be added to a nourishing oil (jojoba, avocado, rosehip, etc.), neutral cream, lotion, or to a basic mask (composed for example of clay, honey or oatmeal). With these preparations various problems concerning the skin of the face and body can be treated (oily and impure skin, redness, eczema, dermatitis, expression lines, scars, stretch marks, etc.). For facial treatments, low percentages of essential oil must be used (1-3%) and only for impromptu preparations. A gentle circular motion of the fingers is often enough for the oils to absorb. Hair can also benefit from adding a few drops of essential oil to the water intended for the final rinse or to a mild shampoo. They can also be prepared nourishing compresses for the skin based, for example, on almond oil or jojoba oil, or balancing sebum or anti-dandruff lotions.
- Bathrooms: the aromatic bath is one of the simplest and most pleasant ways to use it. Essential oils are not miscible with water and therefore tend to form drops on the surface or bottom, then coming into contact with substantially pure skin and mucous membranes. It is therefore necessary, before adding the chosen oils to the bath water, to dilute a few drops in a dispersant, using for example whole sea salt (already detoxifying and draining in itself), honey (moisturizing and soothing), or a soap neutral liquid. Generally 12 drops of essential oil are used for an aromatic bath, but the amount can vary depending on the irritating potential of the oil used; however, essential oils that are particularly irritating to the mucous membranes should be avoided. In addition to the beneficial relaxing and toning effects, aromatic baths can also be useful for relieving ailments such as skin irritation, nervous tension, muscle aches, headaches, circulatory problems, water retention. With the same methods described above for aromatic baths it is possible to make foot baths or hand baths.
- Diffusion in the environment: a pleasant way to perfume the room is to use an aroma vaporizer, or aromatic diffuser, or by pouring a few drops of essential oil into the water tank of the radiator. In this way it is possible to create different, relaxing or invigorating atmospheres, keep insects away, purify the air from unpleasant odors, help keep the environment free from germs; they can also be used in the bedroom, at night, to promote breathing or to help sleep.
- Inhalations: very useful method in case of sinusitis, throat and chest infections; pour 5 drops of essential oil (eg eucalyptus, thyme, peppermint) into a container of very hot water and, covering the head and the container with a cloth, breathe in the steam for a minute, repeating several times. A certain amount of essential oils can also be inhaled by taking a long hot bath, breathing in the vapors of the water, although obviously in this case the amount of essential oil will not be concentrated.
Essential oils are classified into three different groups according to their degree of volatility, or the persistence of their aroma; in fact they differ in the speed with which the oil tends to evaporate when exposed to the air: highly volatile essences such as basil or eucalyptus evaporate very quickly; on the contrary, low volatility essences, such as incense or patchouli, evaporating very slowly, have a persistent fragrance and are used to maintain the aroma of the more volatile ones for longer.
This classification derives from the intuition that the French Piesse had in the 19th century, who associated the concept of musical harmony with the field of perfumery, classifying the essences precisely on the basis of their volatility and equating them to the notes of the musical scale. Today, the three large groups of top (high), heart (medium) and base (low) notes remain of that detailed classification, which are the fundamental ones for the creations of perfumers: a perfume that does not contain all three. the notes do not have the right harmony; this theory is also applicable to aromatherapy and personalized remedies.
The volatility determines a temporal development of the perfume according to the olfactory pyramid: the top notes are the first to be perceived but also the first to volatilize, followed by the heart notes and finally, after a few hours, the base notes.
Top notes: belong the extremely volatile essential oils, which evaporate very quickly, whose fragrance, generally very fresh and often with fruity tones, is immediately perceptible; examples of essential oils that belong to this category are: orange, bergamot, lemon, grapefruit, mandarin, eucalyptus, mint, tea tree oil, litsea. They act quickly and generally have a stimulating action.
Heart notes: they are the most powerful notes, those that create the trail or the "heart" of a perfume. It includes moderately volatile essential oils, perceptible after the first impression received from the top note; they are characterized by a soft and intense fragrance, often with floral tones such as chamomile, lavender, neroli, rose, jasmine, geranium, ylang-ylang, lemon balm, myrtle, clary sage. The essences that fall into this group generally have rebalancing effects.
Basic Notes: this includes the low volatile essential oils, which emerge more slowly but remain for a long time, characterized by a generally very intense, warm and penetrating fragrance; this class includes most of the essential oils extracted from woods, resins and spices, such as cedar wood, sandalwood, incense, patchouly, myrrh. They generally have relaxing effects.