1. Different views on the toxicity of essential oils

Different people and organizations have different philosophies. The knowledge deficits of aromatherapists and authors of aromatherapy publications, as well as concerns about public misuse, are responsible for a variety of claims regarding the toxicity of essential oils.
1.1 Different philosophy

According to the concept proposed by Daniel Penoel, we regard the holistic aromatherapy as a basic energy attribute. This idea, first proposed by the Frenchman Maugerite Maury in the 1930s, has become the mainstream of aromatherapy in English-speaking countries.

Use relatively small doses of essential oils, generally no more than 2.5% in massage oils, the main therapeutic effect may be a secondary "energy" or just "local" effect, these effects and acupuncture or homeopathic The therapeutic effect is similar, and is the result of the action of aroma molecules on the olfactory bulb.

The whole aromatherapy originated from beauty therapy, and the training of aromatherapists is still limited to massage and other application methods today, rather than in-depth study of the chemistry and pharmacology of essential oils and the history of the application of essential oils in traditional medicine.

In her book "Guide to Aromatherapy," Maury claims that she avoids using essential oils as a drug, including oral administration. She thinks this is a matter for professional physicians.

Affected by Maury's above work, the overall aromatherapy continues to develop, especially in the UK, where the famous aromatherapists are Marceline Arcier and Daniele Dyman. We have found that a special creed (dogma) is drawn from the field of beauty therapy, that is, aromatherapy is a kind of mitigation therapy derived from the energy point of view. Emphasizing the use of small doses of essential oils and avoiding oral and other high-dose applications, this particular bias has long been recognized as the philosophical basis for the widespread view of essential oil toxicity.

On the contrary, the French physicians include naturopathic practitioners (natural medicine refers to the use of drugs, the use of air, sunlight, water, heat, etc.) and herbal medicine practitioners advocate the aroma - The medical method is more practical and reasonable. The "French-style" method mentioned in the book "Aromatherapy" published by RMGattefosse in the 1930s often uses essential oils in large doses, both internally and externally, to produce a dose-dependent pharmacological effect. Aromatic-medical methods require an in-depth understanding of the chemical structure of essential oil components and the pharmacological and toxicological effects of essential oils, allowing aromatherapists to determine safe doses and prevent side effects during use. Therefore, I believe that It is more scientific to determine the recommended dose of essential oil based on pharmacological effects.
1.2 Limitations of knowledge

As I mentioned earlier, the training of whole aromatherapy has not made any in-depth considerations about the chemical composition of essential oils and their known pharmacological effects. The recommended doses and side effects of essential oils described in the aromatherapy literature are based on incomplete or one-sided understanding of existing knowledge.

Much of the discussion in many publications is the product of a one-sided understanding of various materials. If the authors are not clear about the side effects of certain essential oils, then he may list as many side effects as possible to avoid people using them or using them in large doses. Excessively even listing non-authentic side effects may be considered a laudable thing, but these exaggerated arguments have had negative consequences, that is, it is widely believed that the use of essential oils can be extremely dangerous.

I personally think that those who call themselves aromatherapists should be proficient in the proper use of essential oils and be familiar with their potential toxicity, just as we generally believe that people who are medicinal in herbal medicine must be familiar with universal prescriptions.
1.3 Public misuse of essential oils

A large number of aromatherapy books are written for laymen. In this regard, the authors generally believe that the recommended doses of special attention and the use of those substances should be avoided, thereby avoiding possible side effects and litigation arising therefrom. Therefore, the recommended dose of essential oils is extremely low, and those that are considered possible, such as pregnant women, are listed under each essential oil without exception.

When we look at these aromatherapy books, we find that these publications, which are easily distributed to the public, are often used as training materials for aromatherapists. After in-depth research, we will also find that the publications provided to practitioners and health professionals are similar and make many of the same recommendations. What are the reasons? I think aromatherapy still needs to go beyond just treating sadness to restore a good level of sensation. Just like the standard set of procedures that herbal doctors have trained and practiced, training aromatherapists is comprehensive and involves a variety of pharmacological effects of essential oils. Such comprehensive knowledge includes both the positive effects of essential oils and their side effects.

2. Toxicity of essential oils

The most commonly used test for measuring potential toxicity to humans is LD50, a semi-lethal dose. This procedure routinely uses experimental animals to test certain compounds used as drugs, agrochemicals, flavorants, household fragrances, and cosmetic ingredients. Toxicity. During the test, the experimental animals used were generally rats, and the dose of the compound administered to the rats was even half of the total number of rats tested. Then calculate the ratio of the grams of the test compound to the body weight per kilogram of the test animal is the semi-lethal dose, such as LD50 is 1.0, that is, 50% of the test animal death is 1g per kilogram of body weight, if we regard ourselves as In the case of a large rodent, this is equivalent to a lethal dose of 60 g for an adult weighing 60 kg.


Excluding ethical factors, since no effective alternative animal experiments have been found so far, we consider the above test values as acute oral lethal dose and lethal dose, ie LD50 represents a full oral dose or a direct test of the test compound. A semi-toxic dose resulting from injection.



In addition, experimental animals were also used to study chronic toxicity, ie, long-term toxicity, and dermal toxicity, that is, toxicity produced after high-dose administration to the skin. Chronic toxic doses are always lower than the corresponding acute toxic doses, and dermatological studies have produced conflicting results, and animal skin tests are not completely similar to human exposure results. In terms of the most common application of essential oils in aromatherapy, we are most concerned with acute LD50.

Misunderstanding of essential oil LD50 during the application of aromatherapy: When we evaluate the acute toxicity of essential oils such as wintergreen oil (mainly containing methyl linoleate) or eucalyptus essential oils (mainly containing 1,8-eucalyptus), animals LD50 can be used as a participatory indicator of the potential toxicity of essential oils. An essential oil, such as thuja oil (Thuja occidentalis), has an LD50 of 0.83 for an animal and a semi-lethal dose of 50 g for an adult weighing 60 kg. This is a very large dose, in fact, people have already had a serious poisoning reaction at the 10g dose.



I reiterate that we assess the toxicity of essential oils based on acute oral toxicity, a lethal dose of a single oral dose. Mistakes in aromatherapy applications related to their toxicity often appear in the following two areas.

2.1 Dose of essential oil
The amount of essential oil used in massage oils, bath oils, household deodorants or inhalants is generally only a small fraction of its toxic dose. For example, rat acute oral wintergreen oil has an LD50 of 1.2, but wintergreen oil may be more toxic to humans. Based on several cases of overkill in the past few years, we estimate that holly oil has a LD50 of 0.3 for humans. For adults weighing 60 kg, this is equivalent to taking 18 g of wintergreen oil. If you want to treat back pain with a 2.5% preparation containing wintergreen oil, use a 1ml massage. 1 ml x 2.5% = 0.025 g of methyl salicylate, 0.025 g of hydrazine 18 g (LD50) = 0.00139 or 0.139%. Therefore, the actual amount of essential oil is only 0.139% of the lethal dose, or 700 times less than the lethal dose.



If we increase the use of 2.5% wintergreen oil, the dose we receive will increase. If 10ml is used at a time, it is equivalent to 0.25g or 250mg of wintergreen oil. If all the wintergreen oil is absorbed, the amount of 250 mg of methyl salicylate is equivalent to the amount of salicylic acid contained in one piece of aspirin. Conventionally, wintergreen oil and sweet birth oil are avoided in aromatherapy, even for trained aromatherapists, and all members of the International Federation of Aromatherapy (IFA) swear no oath. Use wintergreen oil.



We also found some puzzling phenomena, that is, the public has not been able to buy many topical skin preparations containing methyl salicylate (10-30% methyl salicylate), but few adverse reactions have been heard. Report. Patients taking anticoagulants such as warfarin should avoid methyl salicylate, even if it is used externally.



Even if this relatively toxic compound (I believe that any essential oil with an LD50 of less than 1.0 falls within this range, it can be used as an effective anti-inflammatory agent without potential toxicity.

2.2 Different routes of administration of essential oils
We must not only consider the dosage, but also the application of essential oils. After oral administration, essential oils are generally absorbed and quickly absorbed into the blood circulation through the portal vein. Other routes of application of essential oils are not as high as the oral route. Table 1 lists the potential toxicity of each pathway, which is a good indication of the relationship between dose and absorption.

Table 1 Potential toxicity of several essential oil application routes

Based on the conclusions of the above table, we also understand that the relatively toxic pennyroyal oil can be administered as a safe and effective mucolytic substance by inhalation. The amount is high, but the typical dose is always small. When topical skin is applied to essential oils, we cannot assume that all essential oils are absorbed. If the site of administration is not covered, it is usually different from the topical application in aromatherapy, and the dose is greatly reduced due to the volatilization of essential oils.



Bronaugh et al. found that when various fragrances were applied to the skin and covered, 75% of the dose was absorbed by the body; if the fragranced parts were kept exposed, the absorption of hydrazine decreased to 4%.
It has now become clear that essential oils are applied to the skin through the epidermis after application to the skin, but further research is needed in this area on various factors that affect skin absorption, such as the type of essential oil compound, the matrix of the carrier used, and various factors of temperature. How it affects the amount of transdermal absorption. The amount of essential oils reported in the published research results varies widely. D-pinene is the main component of most citrus oils; the Hotchkiss study found that when D-pinene was used in human tissues, the absorption rate was only 2%.



When a formulation containing 2% true lavender oil (Lavandula angustifolia) is applied to the abdomen of a volunteer, about 10% of the substance is absorbed into the systemic blood circulation. At the same time, the absorption rate is relatively fast, and the blood concentration reaches a peak after 20 minutes of skin administration. After 90 min, the concentration of linalool and linalyl acetate (the main component of lavender oil) dropped to almost zero, indicating that these substances were almost completely metabolized.



Bronaugh measured the transdermal absorption rate of benzyl alcohol, benzyl acetate and benzyl benzoate using rhesus monkey as an experimental animal. These three compounds are the natural components of ylang ylang oil. After the substances are formulated into a moisturizing emulsion applied to the bare skin of rhesus monkeys, the total absorption rate is easier to transdermally absorb benzyl acetate, which may be the skin of rhesus monkeys covered with hair follicles, which will absorb the essential oil more effectively.



Based on the above research results, when an essential oil is applied to the undamaged skin by using vegetable oil as a carrier or as a cream and gel, and it is kept exposed, it is conservatively estimated that the body absorption will not exceed 50%. As mentioned in the example of wintergreen oil, the absorption is originally 0.025g. According to the current inference, it should be half of the absorption, ie 0.0125g. According to the current inference, it should be half of the absorption, ie 0.0125g, lower than the oral poisoning dose. 1/1400.



This is related to the most commonly used aromatherapy such as massage and OTC (over-the-counter) topical preparations (such as sputum containing methyl salicylate). If the skin has been damaged, the stratum corneum of the damaged part is no longer present. At this time, it is necessary to carefully consider that all the essential oils will be absorbed.
2.3 The importance of the dose
There are many essential oils in the aromatherapy book that are listed as “not for therapeutic purposes”. These essential oils include hyssop oil, peppermint, tansy oil, arborvitae, wintergreen oil and moss. Wormwood oil, etc. However, many scientists know that these essential oils can be safely used as long as they are used in strict accordance with the recommended dosage and application method. Thus, the importance of the dose of essential oils in aromatherapy applications.



3. Essential oils and pregnancy

The use of essential oils during pregnancy may be the most sensitive area of aromatherapy, which has led to a variety of highly conservative discussions. More general advice from the use of essential oils during pregnancy to the use of the most non-toxic essential oils in very small doses. Most aromatherapy literature clearly states that essential oils with "emmenagogic" effects, ie essential oils that may affect the menstrual cycle, should not be used during pregnancy.



This prevailing practice may be due to the philosophy of “doubt not to use” and the misuse of various toxic parameters, fear of public misuse and legal proceedings arising therefrom. In addition, the lack of understanding of the hormones and physiological processes during pregnancy is one of the reasons.

The effects of essential oils on pregnancy involve the following three aspects:

Certain essential oils may damage developing fetuses [such as teratogenicity]. Causes fetal reabsorption or birth defects.

Certain essential oils can cause abortion or miscarriage/premature.

Essential oils that can affect hormone levels interfere with fertility or affect normal pregnancy.





3.1 The effect of essential oil dose on pregnancy
A large number of reported cases involving severe high-dose essential oils causing severe poisoning or death of unborn babies, all of which are invariably pointed out by the fact that pregnant women are taking large doses or poisoning doses of certain special essential oils, especially those rich in menthol. Peppermint oil, which is metabolized in the body to a highly toxic furan epoxy compound, menthofaran, and parsley seed oil, which is rich in dimethyl alcohol-containing apiol, which can cause Fetal abortion, this kind of compound is actually a very bad abortion (abortifacient). Women often experience severe poisoning after oral administration, sometimes fatal poisoning, and sometimes do not cause fetal abortion.



Guun completed the study of human isolated uterus exposed to essential oils commonly used as abortion agents such as Juniper oil, eucalyptus oil, rue oil, savin oil and tansy oil. These tested essential oils did not directly stimulate the uterine muscles (the uterine muscles are stimulated to cause fetal paralysis and may be premature). Another study also showed that such essential oils do not directly cause fetal death and cause spontaneous abortion.



It is the only abortion agent when it is taken in large doses. It causes acute liver poisoning (liver injury) and causes termination of pregnancy. Oral administration of up to 7.5-10 ml of peppermint oil will not cause miscarriage. The lowest dose of celery brain abortion is equivalent to taking 1.5-6 ml of parsley oil every day for 8 days.



It is well known that when many authors of aromatherapy publications use a small portion of a highly toxic dose as a safe dose, their understanding of the toxicity of essential oils is incorrect. Recently, I have seen some specifications for atomized essential oils for fresh and disinfected air in the care room. The instructions suggest that any essential or toxic oils should not be used in places where pregnant women are resting.

Let us recall that the example of inhaling the aroma of the peppermint oil, that is, 10% of the peppermint oil is used together with plant essential oils such as Eucalyptus radiata and sea pine. We also use an aerosol generator for each The above-mentioned mixed essential oil is sprayed at a rate of about 1 ml per hour, and the aroma of the spray is inhaled for 15 minutes three times a day, and it is assumed that the body absorbs up to 50% of the essential oil. According to the above conditions, we can obtain the following results:

15min × 3 times = 45min × 1.0ml / h = 0.75ml discharge

0.75ml × 50% absorption rate = 0.375ml possible inhalation and absorption

0.375 ml × 10% (concentration of walnut oil) = 0.0375 ml. That is about 35ml of peppermint oil

Human LD50=0.4 for walnut oil, for adults weighing 60kg, equivalent to 24g walnut oil

35mg ÷ 24g = 0.14%, which is 0.14% of the semi-lethal dose

This value does not even reach 1/700 of the poisoning dose.



Of course, this is a small dose, if the essential oil mixture is sprayed throughout the indoor space, a small fraction of the 35 mg of peppermint oil may be absorbed. There are many examples of such an example. For example, 12.5-25 mg of tar, spit on the meat mites to kill papillra wart virus, and camphor-containing rosemary oil and methyl black pepper phenol-containing basil oil are formulated into a concentration of 5%. Relieve low back pain in the third phase of pregnancy. The doses used in the above two examples are much lower than the acute and chronic toxic doses.