by Robert Tisserand
The importance of dilution before applying essential oils topically is being increasingly recognized by both consumers and corporations, and yet “dilute before use” or similar is insufficient safety advice for some essential oils. Diluting cinnamon bark oil to 20% for example, may not protect you if it needs to be diluted to 0.1% to avoid an adverse reaction.
Risk vs benefit
Adverse reactions to herbal preparations are as old as plant medicine; Dioscorides refers to several in his herbal text, written 2,000 years ago. And perhaps it makes sense that if something is a strong medicine, then it may cause problems for some people. Cinnamon bark oil is quite a potent substance, due to its high concentration – around 80% – of cinnamaldehyde. Some of the outstanding properties of cinnamaldehyde are highlighted below, along with the number of research articles (citations) found in the medical database PubMed in October 2015.
Cinnamaldehyde research on PubMed
Topically allergenic / irritant
One of the most potent antibacterial constituents in essential oils.
A very potent antifungal too.
No human trials, but this strongly suggests a potential.
Promising research, some clinical.
Cinnamaldehyde has some beneficial properties, but allergies are undesirable, so the challenge is to identify a dose or dilution that is effective, and also safe for at least 99% of us. Since nothing is totally risk-free, this may require a trade-off between risk and benefit, but generally, we look to minimize risk. And let’s be clear about one thing – if we’re going to assume that the benefits of cinnamaldehyde apply to cinnamon bark oil, which is quite reasonable as it’s 80% of the oil, then we also have to assume that the adverse effects of cinnamaldehyde apply to cinnamon bark oil. If you want to rule out the research on adverse effects because the cinnamaldehyde used in the research was made in a lab, or because the tests were done on isolated cells or animals and not humans, well then that will also rule out most of the good stuff.
Also, the adverse reactions being discussed here relate to the skin, and we have not explored the potential for cinnamaldehyde-rich oils to irritate mucous membrane, though there certainly is such a potential. In a review of cinnamon, cinnamon oil and constituents, Navabi et al (2015) comment: “Despite the above reported studies that promote the use of cinnamon applications in food and cosmetic products, the oral ingestion or skin application of cinnamon or its components (i.e. cinnamaldehyde, eugenol and cinnamic acid) is not always advisable and is recommended only in very small doses.”
Haptens and adverse reactions
In the aromatherapy world, the most common type of adverse reactions are skin reactions to topically applied oils. Adverse skin reactions (ASRs) are also one of the most obvious types of adverse event – when it happens you can feel it, and others can see it. ASRs are divided into four broad categories:
It has been said that it’s impossible to have an allergic reaction to essential oils, because they do not contain proteins, and only proteins can cause allergies. However, an allergen is a substance, protein or non-protein, capable of inducing allergy or specific hypersensitivity.
Our immune system can’t recognize very small molecules such as those found in essential oils but, perhaps unfortunately, haptenation gets around this. The concept of a ‘hapten’ emerged from a series of articles by Landsteiner & Jacobs beginning in 1935, and is Greek for ‘to fasten’. Some essential oil constituents, such as cinnamaldehyde, can cause allergies because they are haptens. This means that they are ‘protein-reactive’; they bind with proteins in the skin. More specifically, they bind with peptides (short chains of amino acids) on the surface of Langerhans cells, and the Langerhans cells then migrate to local lymph glands, where the peptide-allergen complex is presented to T-lymphocytes. Antibodies are then created, and the next time the same hapten contacts the skin, an allergic reaction is almost inevitable.
Cinnamaldehyde is the most widely studied essential oil allergen. We know for example that it activates a signaling system in Langerhans cells, and this is what causes them to become active and migrate from the epidermis to local lymph nodes (Ouwenhand et al 2008). This migration is an essential step in the allergenic process.
Irritation reactions are quite different to allergic reactions, as they do not involve the adaptive part of the immune system. If your skin becomes inflamed after applying an essential oil, applying a vegetable oil may help to calm down any type of adverse reaction, especially an irritant one. However, if you have had an allergic reaction you cannot take away the antibodies you now have. You have acquired an allergy to an essential oil constituent, for life. Topical allergies sometimes do fade, in a similar way that you may need a boost for an immunization after 10 or 20 years because your immune system no longer produces antibodies. But usually it’s that kind of time scale – decades. And it might never fade. Better than waiting to see if your skin becomes inflamed is to prevent it from happening at all, and the best way to do this is to understand appropriate dilution.
Our cinnamon oil survey
The Tisserand Institute conducted a survey in order to find out more about ASRs to essential oils as used by aromatherapy enthusiasts, and I co-authored the subsequent Special Report with Kelly Ablard and Christine Carson. We selected cinnamon bark and cassia oils for this survey since both are high in cinnamaldehyde, and this constituent is regarded as a potential irritant and allergen by dermatologists. Since 1995, 270 of 14,007 dermatitis patients who were patch tested with a 1% concentration of cinnamaldehyde had an adverse reaction to it (See Cinnamon Survey Special Report). That’s a little under 2% of those tested, and this makes cinnamaldehyde the most high-risk essential oil constituent known from patch testing (Tisserand and Young 2014, p93).
There are accounts in the dermatology literature of adverse reactions to cinnamon bark oil applied to the skin. Repeated use of diluted cinnamon oil has caused allergic contact dermatitis (Ackermann et al 2009, Calnan 1976, Sánchez-Pérez and García-Díez 1999), and use of undiluted cinnamon oil has caused irritation (Perry et al 1990). One case was so severe that it was classed as a 2nd degree chemical burn (Sparks 1985).
In our survey, we found a very high incidence (27%) of reported adverse reactions to cinnamon bark or cassia essential oils, and we found that using undiluted essential oil on the skin did increase the risk of adverse reaction. Another risk factor, as well as dilution, is frequency – the more often you apply the same substance, the greater the risk. This combination of risk factors seemed to be borne out in the results of our survey,
Our survey did not directly address the issue of why one person can use undiluted cinnamon bark topically and not experience an adverse reaction, while another will react to a 5% dilution. However, we did find an interesting correlation. We found that people with seasonal allergies are six times more prone than average to adverse skin reactions to cinnamon bark and cassia essential oils. There may possibly be a genetic reason for this.
Our findings suggest that, for many brands, there are insufficient safety guidelines on the labels of these essential oils. Label information was not part of our survey, but we believe that advising non-specified dilution, which seems to be common, does not provide sufficient protection for consumers for these two oils. Based on our survey results, we suggest that a recommended maximum dilution of 0.1% should be adopted within the aromatherapy industry. That’s equivalent to one drop in 30-40 ml.
What cinnamon oil retailers in the USA currently recommend
For the purposes of this blog post, I looked at 30 retail suppliers of cinnamon bark oil, to see what safety advice for topical application was given online (Table 1). I found that generally there is a very high level of awareness that this essential oil presents some risk, with two out of three referring to it as a potential irritant or sensitizer. No supplier seems to suggest that dilution is not required before application to the skin. However in this list, only the first 19 (63%) either prohibit use on the skin completely, or specify a dilution. The remaining 11 suppliers (37%) recommend diluting the oil, but without stating by how much.
It’s clear from this exercise that there is an enormous range of recommended dilutions being given, including 0.07% and 20% – a difference of almost 300 times. I believe this needs to change, and I am especially concerned that the two largest retailers, Young Living and DoTerra, are among those that only suggest non-specific dilution.
Table 1: Retail suppliers of cinnamon bark oil and online safety guidelines
Table 1 includes retailers based in the USA. It may not be a complete list, but it is representative of the range of guidelines given for cinnamon bark oil. This information was obtained from online searching, and it is possible that product labels have different guidelines.
The importance of essential oil dilution
There are safety guidelines that exist in order to minimize ASRs. The International Fragrance Association (IFRA) has a voluntary code for the fragrance industry, and began issuing guidelines in the early 1970s. These are based on testing carried out by a sister organization called RIFM, which includes tests on panels of human volunteers. For example, patch testing on a panel of 25 volunteers by RIFM using cinnamaldehyde produced reactions in two of the 25 when tested at 0.5%, but 11 people when it was tested at a 2% dilution (Opdyke 1979). This is because ASRs are dilution-dependent; the greater the concentration of the substance on the skin, the greater the risk.
Safety guidelines exist to protect those who would likely have an adverse reaction, and in many cases this is a minority. Whether it’s 1%, 5% or 10% of people it’s a minority, meaning that most will not experience that particular adverse reaction. This of course does not mean that a safety guideline is wrong or can be ignored. In recent years, I have come across many reports of adverse skin reactions from aromatherapy enthusiasts applying undiluted essential oils topically. These reactions may not happen for a while – weeks or months in some cases, and maybe never – but if and when they do, they are not pleasant.
Using undiluted essential oils on your skin may be reasonable for some essential oils, for some problems, and for some people. But generally it’s not a good idea because of safety issues. Using concentrated essential oil may not even be useful, but it depends on what you are trying to achieve. Table 2 is a general guideline for essential oils, which should keep you as safe as possible while retaining therapeutic effect. There are also guidelines for high-risk essential oils such as cinnamon bark, as well as for specific age ranges, which can be found in Essential Oil Safety.
Table 2: General guideline for essential oil dilution
|End use||Dilution range|
|Bath & body products||1-4%|
|Acne lesions, insect bites,
fungal nail infections
Dilution cannot be overemphasized when it comes to all essential oils, but is especially important for cinnamon bark and cassia. A little really does go a long way and if you proceed with caution, you may be able to benefit from some of the amazing properties of these oils for longer, and with no adverse reaction.