Very few oils can be used undiluted on the skin. In most cases, they will be diluted in vegetable oils, making creams and gels, even powders. Craft and art that should be approached studiously and with a lot of love, all for the purpose so that the oil would not be harmful and that the application of the oil would be pleasant and simple.
Dermal preparations are formulations intended for use on the skin, and sometimes the mucous membranes of the urogenital system. Although dermal use is mainly associated with achieving healing effects on the skin, it should always be borne in mind that the molecules of essential oils very easily pass through the skin into the bloodstream. Therefore, an effect is achieved on the desired organ system or the whole body. The sale is almost entirely dominated by preparations with essential oils that act on organs other than the skin – antirheumatic gels, peppermint oil for migraines, oils and gels for better circulation, gels with eucalyptus globulus and similar oils that help with respiratory infections- just a few examples of such use.
Pure essential oils
A small amount of essential oils can be applied directly to the smaller surface of the skin. These are usually mild oils that do not irritate the skin, such as lavender, tea tree and ravintsara. More sensitive areas of the skin such as the neck, face, genitals, near the eyes, and skin near the mucosa in general should be avoided. A typical and very common mistake in application that I have encountered in practice is the application of pure tea tree essential oil all over the face due to acne. It is easy to find information on the Internet that pure tea tree essential oil can be applied to acne. This is only conditionally true, as it can be used topically at the site of inflammation, and for a shorter period of time. Applying to the entire surface initially causes milder redness, and after repeated applications, the redness intensifies with the appearance of pronounced dryness of the skin.
The use of pure tea tree essential oil for feet fungal infections is somewhat more justified. It should also be accepted cum grano salis. Namely, some people may be more sensitive to repeated use of pure essential oils with the appearance of xerosis (dry skin), erythema (redness), and later even allergic reactions. Therefore, even for the example of tea tree, it is better to use formulations that do not have to be complicated. For example, for a fungal foot infection, a simple formulation of 50% tea tree and 50% castor oil is quite sufficient to reduce possible side effects, and even works better than pure tea tree due to the antifungal action of castor vegetable oil. An even more complex formulation will include powders or gels.
Pure essential oils can be used for onychomycosis, i.e. fungal nail diseases, since vegetable oils do not enter into the nail structure easily.
In aromatherapy practice, there are examples of applying some essential oils, such as ravintsara, in very large doses (50mL and more), directly to a large area of skin. This is independently described by Dominique Baudoux and Dr. Daniel Pénoël for cases of severe infections. But this is reserved exclusively for professionals and in no case should essential oils be applied in this way without medical supervision.
Essential oils in vegetable oils
To avoid skin irritation, essential oils are mostly dissolved (diluted) in vegetable oils. The most commonly used oils are those that penetrate the skin relatively easily, such as macadamia, kukui oil, apricot, hazelnut and almond.
Concentrations of essential oils vary from 1-50%. They are extremely rarely used in higher concentrations of 90%, for example in onychomycosis. But how many essential oils are used for individual types of applications? This will depend on the chemical composition of the oil, as irritating essential oils are, logically, applied in a lower concentration, and it will depend on the application surface. The surface of the application depends on why we apply the essential oil. Local treatment of the wrists in rheumatoid arthritis is an example of a relatively small body area. Applying to the back and chest for respiratory problems already represents a larger area, while full body massage is the largest area to which essential oils are applied.
- For the treatment (massage) of the whole body, the concentration is usually up to 5% of essential oils. This general rule ensures that even relatively irritating oils can be well tolerated. Fortunately, a significant number of irritating essential oils such as oregano, clove and the like and do not have a particularly pleasant smell in the context of massage and are not even suitable for it, because an olfactory component is certainly important. But some irritating essential oils can be olfactory pleasing, such as lemongrass and cinnamon bark. In this case, a professional masseur must be well aware of the risk of applying certain essential oils. Fortunately, what stops aroma masseurs in Croatia from using high concentrations of essential oils is certainly their price. Some essential oils are certainly not good for application to a larger area of the body, such as evergreen rich in methyl salicylate and for which systemic toxicity has been described in dermal use.
- For local application on a small area, the concentration can reach up to 50%, but deeper knowledge of oils is also required. It is usually used 10-20%, depending on the type of ailment. As an example we will take peppermint essential oil. ESCOP states that the maximum concentration of menthol and peppermint essential oil should not exceed 16% (w/w, or percentage by weight) for the treatment of joint pain. If we approximate that the essential and vegetable oils have a similar density, and that the batch of peppermint essential oil contains 50% menthol, then the final preparation will be able to have up to 32% peppermint essential oil. For irritant oils rich in phenols and aldehydes, such as thyme chemotype thymol, oregano, cinnamon bark and similar oils the concentration for topical use rarely exceeds 5%. To make a higher concentration, you need a deeper knowledge of aromatherapy.
- For daily facial skin care, the concentration is usually below 2.5%, rarely up to 5%.
What does percentage mean and how is it calculated? All percentages listed here refer to volume percentages. Therefore, the preparations should be done volumetrically, i.e. using pipettes or beakers. However, this is not always practical, so in real professional practice it is best to work gravimetrically, i.e. weighing. The mass is calculated from a simple formula:
mass = density (g/dm3) x volume (dm3)
That is, the mass of essential oil required to obtain a precisely determined percentage by volume of essential oil is:
mass = density (g/dm3) x volume percentage x desired total volume (dm3)/100
Of course, there are also approximate formulas for everyday practice such as aroma massage. The approximation is that 1mL of essential oil makes 20 drops. This formula reads as follows:
percentage of essential oil [%] = 5x (number of drops of essential oil)/(millilitres of vegetable oil)
This means that if I put 20 drops of essential oil in 20 millilitres of vegetable oil, I got a 5% mixture. Conversely, if I want to make 30mL of 5% essential oil, I will use the following formula:
number of drops of essential oil = (percentage of essential oil) x (millilitres of vegetable oil)/5
It should not be emphasised that this formula is very approximate because the size of the drops, and thus the volume, depends on the droppers themselves and the viscosity of the oil.
Anhydrous solid/paste systems
This complicated name indicates balms and salves, one of the first cosmetic formulations probably used for thousands of years. They look like creams, but they are not, because they contain one phase, oil. The simplest balm or salve is obtained by dissolving wax in vegetable oil, with the addition of essential oil depending on the purpose. The most commonly used is unrefined or purified beeswax, but also a whole other range of other waxes, such as carnauba, candelilla, rice wax and similar. After cooling, the wax in the mixture raises the melting point of the whole solution, and the system itself takes on a solid or pasty consistency.
Depending on local preferences, balms have slowly disappeared because they have been replaced by emulsion systems, but they are still popular in the care of dry skin of hands and feet, and lip protection. The wax in balms is not only a thickening agent, but also an occlusive agent, which means that it forms an impermeable film on the skin that protects it from further drying.
Gels build substances that do not dissolve in water but swell to large volume dimensions and their molecules form a networked system. There are various types of gels that you can read about in the natural cosmetics section, and here we primarily mean water gels. Gels are popular because, unlike oil mixtures, they do not leave greasy film on the skin and are immediately absorbed. The most commonly used are either synthetic gels such as carbopol gels and beta gels, which are available in Croatia as ready-made gel bases, semi-synthetic gels cellulose derivatives and natural gels such as red algae gels. The oil concentration in usually up to 5%. Such a low concentration is important because, unlike vegetable oils, which significantly slow down the absorption of essential oils through the skin, gels are aqueous media and the molecules of essential oils want to “escape” into the lipid structure of the skin as soon as possible. Bigger concentrations of essential oils would be therefore too irritating.
Gels can be formulated in the form of pseudoemulsions, where the essential oil is dispersed in water, and coalescence (droplet fusion) and the separation of the essential oil on the surface of the gel is prevented by the very viscosity of the gel. Another way of formulation is the addition of emulsifiers and the formation of real emulsion gel systems.
Emulsion systems are a very diverse group of preparations that differ according to the ratios of fat and water phase. They can be oil-in-water (U-W), where there is more aqueous and less fatty phase, and water in oil (W-U), where the oil phase dominates.
Of course, modern formulations have created far more creative forms of emulsions that can be composed of multiple phases, for example, the emulsion can be WUW, where first the water is emulsified in the fat phase and then the whole system is emulsified in the aqueous phase. Far more about emulsions you can read in the part dedicated to cosmetics. The basic emulsion consists of an emulsifier, a molecule that has a part of the structure that prefers water (hydrophilic), and a part that prefers oil (lipophilic). Such a molecule is incorporated at the interface between the water and oil phases and thus stabilizes the emulsion, i.e. prevents the separation of the two phases.
Emulsions are popular ways of applying essential oils and dominate both in cosmetics and in medicinal preparations for the skin. In addition to being better absorbed by oils, emulsion systems generally better maintain the skin’s hydrolipid balance, giving the skin extra moisture. Of course, the truth of this statement largely depends on the choice of raw materials and the formulation itself. The advantage of emulsion systems is the possibility to use water-soluble and oil-soluble medicinal molecules at the same time. For example, an emulsion system may contain dexpanthenol, a provitamin soluble in water, aloe vera juice which is in itself an aqueous solution, but also evening primrose oil, and chamomile essential oil which is soluble only in oils. In this way, a better effect is achieved, i.e. the synergy of different medicinal ingredients.
Emulsion systems can be of different consistency or viscosity, and this depends on the choice of emulsifiers and other emulsion stabilizing substances. They can be creams, milks, liquid emulsions or have the form of a gel emulsion system. The concentration of essential oils on the total weight of the cream is usually lower, 0.1-3%.
The choice of emulsifier is very important because it depends on what type of emulsion it will be. Also, natural cosmetics use emulsifiers that comply with the COSMOS directives on natural (eco) emulsifiers.
Powders are sympatico preparations with essential oils, almost non-existent in Croatia. Today, we mostly identify powders with decorative or camouflage cosmetics. However, they are also used for medical purposes to treat superficial skin problems, such as fungus, sweating and problems that occur due to sweating, baby care, and for the so-called dry massages in which powder is used instead of vegetable oils. They are made by coating talc, rice starch, kaolin and other types if clay with essential oils, and rest on the property of adsorption of essential oils on the surface of particles. When applied to the skin, the essential oils are deadsorbed (released) and transferred to the skin. In addition to absorbents, powders contain a number of other excipients, such as magnesium stearate, which improves the adhesion of powder to the skin, or highly dispersible silica, which improves the adsorption of essential oils and improves the so-called rheological properties (leakage properties) of powders The adsorption power of talc and similar substances is not unlimited, so the total content of essential oils is 1-3%.
They are a completely new medicinal form of essential oils that is mainly used in cosmetics. They are formed by the mechanical process of spraying essential oils in pure water without the help of emulsifiers, solubilizers and surfactants, whereby they form microemulsions without emulsifiers stabilized by electric charges of particles, and not by emulsifier. So far, solutions of essential oils have mostly been made with the help of emulsifiers, such as polysorbates, or solubilizers such as ethoxylated castor oil (cremophor EL) and labrasol. Essential waters can contain from 0.1-10% of essential oils, but most often it is from 1% down. They are used as pleasant face tonics, as aqueous phases of creams, but theoretically they can also be used in the oral application of essential oils.