Essential oils are highly-concentrated and should never be applied topically without being diluted in a carrier oil.
There is no definitive, "correct" dilution for an essential oil. The proper dilution for an essential oil is subjective based on the specific oil you are using and the intended purpose.
In aromatherapy, the ideal dilution for an essential oil is the lowest possible concentration that provides the intended therapeutic benefit and avoids adverse reactions. In cases where this therapeutic margin between benefits and reactions is low, the essential oil should be avoided.
This article is intended to provide a brief understanding of some helpful considerations when determining an appropriate dilution.
Here is the general dilution guidance often provided by aromatherapists:
If you have been learning about essential oils for a while, you may have encountered contradicting information and exceptions to the guidance above. The dilution guidance above is an appropriate, cursory explanation to promote safe use of essential oils. However, this guidance doesn't tell the full story.
You may have noticed that some essential oils—such as Patchouli—are deemed safe above the dilution listed. And, while not recommended, you may sometimes find that certain essential oils—such as Lavender, Helichrysum, Roman Chamomile, and Tea Tree—are used undiluted in aromatherapy when one drop is applied to a targeted location of the body.
On the other hand, some oils—such as Cinnamon Bark—are only safe below a 0.07% dilution. This dilution is equal to about 4 drops of Cinnamon Bark in 8 fl oz (or 1 cup) of carrier oil. And depending on the specific levels of Cinnamaldehyde, Eugenol, and Safrole in your bottle of Cinnamon Bark, this dilution may be too high.
The truth is that there are many complex and compounding factors to consider when determining the right dilution. There is no "one size fits all" approach. Your understanding of the factors below will help you make educated decisions:
The purpose of diluting essential oils is to lower risk and maintain safe use. And the cornerstone of safe use with essential oils is quality.
Your essential oils should be 100% pure and should contain zero fillers, pesticides, fragrance chemicals, or synthetics. They should be purchased from a trustworthy supplier that provides detailed information about the specific essential oils you purchased. You should feel confident that you are using essential oils free of contaminants and adulterants. (See Essential Oil Quality for more information.)
Also, the age of the essential oil may degrade the quality. Oils are likely to oxidize with age which, when applied topically, can cause adverse skin reactions. (Citrus and coniferous oils oxidize more quickly than other oils. Oxidation can be slowed by keeping oils refrigerated, in amber glass bottles, and in bottles that minimize the surface area exposed to air. When making a cosmetic product, the addition of an antioxidant—such as Vitamin E—may stablize the product from oxidation.)
Toxicity occurs when a compound enters an organism, such as the human body, and reaches a level that has the potential to cause damage. Essential oil constituents can cause toxicity when they reach certain concentrations in the body.
But don't let the word toxicity scare you; all substances are toxic at some level. Even water, which is seemingly innocuous, can become toxic to a person when it is over the level the body can handle. With an understanding of the toxicity of certain oil constituents, you can feel confident in making appropriate decisions.
As an example, Peppermint (Mentha × piperita) essential oil has the potential to cause toxicity based on the level of the constituents menthofuran and pulegone. Due to the typical chemical profile of Peppermint, Tisserand recommends a maximum dermal use level of 5.4% due to toxicity.
Tisserand's maximum dermal use percentages assume a topical application of 30 mL (about two US tablespoons) of a finished cosmetic product (e.g., body lotion, body oil) which includes the essential oil. This 30 mL volume is assumed to be the maximum amount of a cosmetic product application in a single day. This assumption is fundamental to understand.
Keep in mind that the dilution has been calculated to limit the dose to avoid toxicity. If your intended use doesn't make sense under this assumption of 30 mL/day, then a dilution higher or lower than 5.7% may be acceptable. For example, if you know the total topical application volume of the cosmetic, which includes diluted Peppermint essential oil, will be 40 mL/day instead of the assumed 30 mL/day, toxicity is likely to be avoided with a dilution of 4.3% or lower [(30/40) × 5.7]. Similarly, for a total application volume of 10 mL/day, toxicity is likely to be avoided with a dilution of 17.1% or lower [(30/10) × 5.7].
Adverse skin reactions are a type of toxicity. The main types of reactions are irritation, sensitization, and photosensitization. Essential oils rich in phenols and aldehydes are particularly known to cause skin reactions.
Unlike the toxicity calculations above where the dermal limit can fluctuate based on the application volume, the dermal limit should not be exceeded when adverse skin reactions are possible.
With adverse skin reactions, the dose is irrelevant; it is the concentration that is important. The concentration of the product is what will trigger the reaction regardless of the application volume applied and regardless of the area of the skin that is covered.
As an example, Bergamot (Citrus bergamia) essential oil has a maximum dermal use level of 0.4% due to phototoxicity. If a cosmetic product contains a dilution of Bergamot above 0.4%, it is equally phototoxic regardless of whether you cover one square centimeter of your skin or whether you cover your entire body.
The following factors about the consumer should influence your dilution decisions:
The intended area of coverage on the body impacts the dilution. In general, a lower percentage of essential oils should be used when a higher percentage of the body is intended to be covered. And, a higher percentage of essential oils may be preferred for targeted applications.
In cases where adverse skin reactions are possible, the percentage of essential oils should not exceed the maximum dermal use level regardless of the area of the skin that is covered.