Preface: before you say “fear monger” please read the post in its entirety. There have been no reports of cancer being linked to essential oil usage – yet. There are also safe ways to use potentially carcinogenic essential oils, and guidelines are provided below. This post is not meant to instill fear, but create awareness and respect for the essential oils which are mighty powerful tools.
Essential oils are made up of dozens – sometimes hundreds – of chemical constituents. Some of these constituents are potentially carcinogenic; others are anti-carcinogenic; some are neither.
I realize there are many other more dangerous substances out there which also cause cancer, and I would agree that essential oils are not high on the list of potential carcinogens. However, due to the popularity of ingestion that is promoted by marketers in some essential oil circles, the cancer potential needs to finally be addressed. Multiple drops of essential oils consumed on a daily basis are encouraged by some of these marketers – and some of the essential oils used are potentially carcinogenic. It is this kind of regular, long-term use that can put one at risk.
Robert Tisserand states in his book Essential Oil Safety, “There is no evidence that tumors in humans have ever been induced by the use of essential oils. Nevertheless, a few do contain potentially carcinogenic substances, and there is concern that these oils may not be safe to use in aromatherapy.”
This post is intended as a reference point only. You can find additional information in Essential Oil Safety – Chapter 12, Cancer and the Immune System. This chapter discusses this issue at great length, with hundreds of references and research data to support the information therein.
Who is at risk?
Individual susceptibility and exposure level are two main risk factors.
Not everyone will respond to the same substances in the same way – the human body is way too complex for that. One person might consume essential oils on a daily basis for a year before they notice adverse effects; others may feel ill after one ingestion. There are many factors, such as individual diet, overall health, age, and other environmental exposures.
Individuals who are considered higher risk than the average person are:
- people with genetic susceptibility to cancer
- people with a personal history of cancer
- people with a family history of cancer
- those who have occupational exposure to carcinogens
- heavy drinkers
These high-risk individuals need to be extra careful not to over-expose themselves to potentially carcinogenic essential oils.
The longer you have been exposed to high-dose dilutions or oral consumption of potentially carcinogenic essential oils, the higher your risk for developing cancer. There is no exact science to this, as everyone is different. If you are one of the high-risk groups, you need to use extra caution.
Potentially carcinogenic essential oil constituents
Without getting into too much detail about cancer and how it works (that is not the primary focus of this post), some essential oil constituents may stimulate cell proliferation, while others may increase the amount of oxygen radicals. Some constituents initiate carcinogenic action, while others may promote carcinogenic action if initiated by another substance. Other essential oil constituents may exhibit estrogen-like activity. There are many different actions essential oils can take.
According to Essential Oil Safety, “A few chemical carcinogens are so powerful that even a single exposure to a dangerous level is likely to result in cancer” although it typically requires high doses consumed daily over a length of time to induce cancer. Additionally, “the potency of carcinogens found in essential oils can be altered by other constituents, which may enhance or inhibit the development of neoplasia.”
After researching the potentially carcinogenic constituents (such as estragole, methyleugenol, and safrole), I looked up in Essential Oil Safety the essential oils which contain significant amounts of these constituents. This list is a result of that research.
Essential oils which contain one or more potentially carcinogenic constituents
- Anise/Aniseed Pimpinella anisum
- Anise (Star) Illicium verum
- Basil (estragole CT) Ocimum basilicum
- Basil (Madagascan, Pungent) Ocimum gratissimum, Ocimum viride
- Bay (West Indian) Pimenta racemosa var. racemosa
- Camphor (brown, yellow) Cinnamomum camphora, Laurus camphora
- Fennel (Bitter) Foeniculum vulgare subsp. Capillaceum
- Fennel (Sweet) Foeniculum vulgare
- Laurel Leaf Laurus nobilis
- Mace Myristica gragrans, Myristica officinalis, Myristica moschata, Myristica aromatica, Myristica amboinensis
- Myrtle Myrtus communis
- Myrtle (Aniseed) Backhousia anisata
- Nutmeg Myristica gragrans, Myristica officinalis, Myristica moschata, Myristica aromatica, Myristica amboinensis
- Pine (Huon, Ponderosa) Dacrydium franklinii, Lagarostrobos franklinii
- Ravensara Bark & Leaf Ravensara aromatica, Ravensara anisata
- Sassafras Sassafras albidum, Nectandra sanguinea, Ocotea odorifera, Cinnamomum porrectum, Cinnamomum ridigissimum
- Sugandha Cinnamomum cecidodaphne, Cinnamomum glaucescens
- Tarragon Artemisia dracunculus
Properly diluting potentially carcinogenic essential oils
Some essential oils contain a high enough percentage of a potentially carcinogenic constituents that they should be avoided altogether and are included in this list here: Essential Oils to Avoid Using Internally and Externally.
The other essential oils can be used – but with caution. If you choose to use them, please follow these dilution guidelines to be sure you are not putting yourself at risk. Generally speaking, these dilutions are for topical use only, and ingestion should be avoided.
Robert Tisserand says in Essential Oil Safey, “even carcinogens have threshold levels, below which they are not toxic, so the amount and duration of exposure have great relevance.” [bold emphasis mine]
Potentially Carcinogenic Essential Oil Dilution Guide for Topical Use
|Essential oil name and Latin name||Do not exceed this dilution
|Anise/Aniseed Pimpinella anisum||2.4%|
|Anise (Star) Illicium verum||1.75%|
|Basil (estragole CT) Ocimum basilicum||0.1%|
|Basil (Madagascan) Ocimum gratissimum, Ocimum viride||0.2%|
|Basil (Pungent) Ocimum gratissimum, Ocimum viride||0.8%|
|Bay (West Indian) Pimenta racemosa var. racemosa||0.9%|
|do not use|
|Camphor (yellow) Cinnamomum camphora, Laurus camphora||0.25%|
|Fennel (Bitter) Foeniculum vulgare subsp. Capillaceum||1.8%|
|Fennel (Sweet) Foeniculum vulgare||2.5%|
|Mace (East Indian) Myristica gragrans, Myristica officinalis, Myristica moschata, Myristica aromatica, Myristica amboinensis||2%|
|Mace (Indian) Myristica gragrans, Myristica officinalis, Myristica moschata, Myristica aromatica, Myristica amboinensis||4.1%|
|Myrtle Myrtus communis||1.9%|
|Myrtle (Aniseed) Backhousia anisata||2.7%|
|Nutmeg (East Indian) Myristica gragrans, Myristica officinalis, Myristica moschata, Myristica aromatica, Myristica amboinensis||0.8%|
|Nutmeg (West Indian) Myristica gragrans, Myristica officinalis, Myristica moschata, Myristica aromatica, Myristica amboinensis||5%|
|do not use|
|Pine (Ponderosa) Dacrydium franklinii, Lagarostrobos franklinii||0.5%|
|Ravensara Bark Ravensara aromatica, Ravensara anisata||0.1%|
|Ravensara Leaf Ravensara aromatica, Ravensara anisata||1.0%|
|do not use|
|Sugandha Cinnamomum cecidodaphne, Cinnamomum glaucescens||3.3%|
|Tarragon Artemisia dracunculus||0.1%|
Anti-carcinogenic essential oil constituents
Now for the good news…there are essential oils which contain constituents that are anti-carcinogenic. They inhibit one or more stages of a cancer's progression.
This does not mean essential oils cure cancer. Just like it takes several factors for potentially carcinogenic essential oil constituents to cause cancer, it also takes a lot of work for these essential oils to help with preventing cancer.
Sometimes the presence of anti-carcinogenic essential oil constituents can negate the carcinogenic potential of an essential oil. Some have anti-tumoral properties.
Here are some of the constituents which are considered to be anti-carcinogenic:
- citral (geraniol + neral)
- methyl jasmonate
I looked up in Essential Oil Safety the essential oils which contain significant amounts of these constituents. This list is a result of that research.
Essential oils which contain one or more anti-carcinogenic constituents
- Basil (lemon) Oximum x citriodorum
- Basil (linalool CT) Ocimum basilicum
- Bergamot (wild) Monarda fistulosa var. menthaefolia, Monarda menthaefolia
- Cananga Cananga odorata, Canangium odoratum f. macrophylla
- Citronella Cymbopogon nardus, Cymbopoon winterianus
- Clementine Citrus clementina, Citrus reticulata var. clementina
- Copaiba Copaifera officinalis, Copaigera langsdorfii
- Coriander Seed Coriandrum sativum
- Dill Seed (European) Anethum graveolens
- Elemi Canarium luzonicum, Canarium vulgare
- Fir Needle (Himalayan) Abies spectabilis, Abies webbiana
- Fir Needle (Japanese) Abies sachalinensis
- Fir Needle (Siberian) Abies sibirica
- Fir Needle (Silver) Abies alba
- Geranium Pelargonium roseum x asperum
- Ghandi Root Homalomena aromatica
- Grapefruit Citrus x paradisi
- Ho Leaf (linalool CT) Cinnamonum camphora var. glavescens
- Hop Humulus lupulus
- Hemp Cannabis sativa
- Lemon Citrus x limon, Citrus limonum
- Lemongrass Cymbopogon flecuosus, Adropogon flexuosus, Cymbopogon citratus, Andropogon citratus
- Lime Citrus x aurantifolia, Citrus x latifolia
- Mandarin Citrus reticulata, Citrus nobilis
- May Chang Litsea cubeba, Litsea citrata
- Melissa Melissa officinalis
- Myrtle (lemon) Backhousia citriodora
- Myrtle (honey) Melaleuca teretifolia
- Neroli Citrus x aurantium
- Orange (Sweet) Citrus sinensis, Citrus aurantium var. sinensis
- Palmarosa Cymbopogon martinii var. martinii, Andropogon martinii var. martinii, Cymbopogon martinii var. motia
- Palo Santo Bursera graveolens
- Pepper (Black) Piper nigrum
- Pine (Black) Pinus nigra
- Rosalina Melaleuca ericifolia
- Rosewood Aniba rosaeodora, Aniba amazonica, Aniba parviflora
- Tangerine Citrus reticulata, Citrus nobilis, Citrus tangerine
- Verbena (lemon) Lippia alba, Lippia gerinata
- Ylang-Ylang Cananga odorata
For more information, please consult Essential Oil Safety, Chapter 12.
Do you have a question or comment? Leave a comment on this post, post in the FB group, or e-mail me.
Lea Harris is a Certified Clinical Aromatherapist Scholar's Program graduate from Aromahead Institute. This website, and its sister website, LearningAboutEOs, is home to educational advice and information about using essential oils safely. Lea founded and runs the Using Essential Oils Safely facebook group, with hundreds of new members joining each week. Lea is the author of The TRUTH About Essential Oil Safety, and the creator of Safe Essential Oil Labels and the UEOS App. You can find FREE classes here: Free Essential Oil Classes.
Lea received her herbalist certification through The Herbal Academy of New England. Lea is a contributing writer for Natural Herbal Living magazine, and blogs about herbs and natural living on her website, Nourishing Treasures.
Lea is Professional level member of the Alliance of International Aromatherapists.
Businesses, groups, and individuals can hire Lea to consult on safety, product formulation, and more on her website Lea Harris CCA.