2. Essential oil toxicity

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 in the application of aromatherapy：

When we evaluate the acute toxicity of essential oils such as wintergreen oil (mainly containing methyl sulphate) or essential oils of eucalyptus (mainly containing 1,8-eucalyptol), animal 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.

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.

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.