Phenol sensitivity and essential oils rich in phenylpropanoids; terpenes might be better tolerated.

Essential Oil Book club - David Stewart; Lists of essential oils and the type of terpene or phenolic compound they contain.

Jan 06, 2025

Someone with certain gene differences, or someone who was overly acidic and therefore detoxing sulfates and salicylate poorly might be sensitive to foods or essential oils that are rich in polyphenols or phenolic compounds like phenylpropanoids - generally helpful to health, but not if you can’t deactivate and remove them properly. We detoxify salicylates less well if overly acidic, lacking in glycine, and/or genetically susceptible and low in methyl folate.

Diffusing Eucalyptus essential oil was reported in one case study as possibly causally linked to hearing damage.. but I am not finding the link in my notes now and can’t find it on PubMed, so likely not a strong link. Eucalyptus isn’t much of a salicylate source compared to wintergreen or birch essential oils.

Topical use of wintergreen oil has caused salicylate excess. (Chan, 1996) Chan TY. The risk of severe salicylate poisoning following the ingestion of topical medicaments or aspirin. Postgrad Med J. 1996 Feb;72(844):109-12. doi: 10.1136/pgmj.72.844.109. PMID: 8871462; PMCID: PMC2398362. https://pmc.ncbi.nlm.nih.gov/articles/PMC2398362/

*This has been in my drafts since November and the topic became part of the ototoxicity series.

Phenols are a ring-shaped molecule formed from 6 carbons typically with one hydrogen attached at each carbon. Benzene, a toxin to health, is the most basic 6 carbon, 6 hydrogen structure. It is chemically very stable making it hard to break down.

Terpenes have a base shape that is different from phenols and would be broken down differently

Salicylates are a known ototoxin and salicylate excess or sensitivity is often misdiagnosed as something else, leaving the underlying problem continuing to cause damage.

Phenol sensitive? Essential oils to avoid.

Some of the essential oils have one primary phenol in large amounts, while others have a combined total of a few phenols making up the percentage listed in the graphic.

Essential oils rich in phenylpropanoids or other phenolic compounds include the following: Basil, Birch - 85-95%, Cinnamon - 20-30%, Citronella - 19-27%, Clove, Cumin, Fennel - 52-80%, Nutmeg, Oregano, Peppermint, Tea Tree, Thyme, Wintergreen. Tarragon - 65-85%. Ylang ylang - 6-10%. Cassia - 4-10%. Lemon eucalyptus - 2-21%. Eucalyptus - 2-3%.

And contain the phenolic compounds: Anethole (fennel), Borneol (citronella), Carvacrol (oregano), Cinnamal (cinnamon), p-Cuminol (cumin), Estragole (basil), Eugenol (clove), Menthol (peppermint), Methyl salicylate (wintergreen and birch), Myristicin (nutmeg), Terpinen-4-ol (tea tree), Thymol (thyme).

(page 267, Stewart, 2005, Read online, internet archive)

Many essential oils have salicylates or other phenols which might affect some people more than others due to dysfunction in breakdown of phenols. Salicylates and phenols are chemically similar.

Essential oils can help health and reduce inflammation and help heal tissue – just use caution as they are potent. Each drop represents a lot of plant material or wood that was gently heated in a big metal container rather than being burnt, and the heat releases the fragrant volatile oils from the plant biomass, whether flowers, leaves, or wood chips. The very small molecules are light weight compared to bulky polyphenols or carotenoids which are often colorful pigments in our plant food.

Essential oils contain primary categories of beneficial chemicals, three of which work together synergistically to improve health by supporting receptor function and in other ways. The phenols are one of the three categories to include in a blend designed for health benefits, smaller amounts might be tolerable while larger amounts might cause symptoms of phenol excess which can be similar to mental/ADHD like symptoms seen with salicylate excess. The excess may be harmful to hearing too.

Non-phenol essential oil categories to include in the trio power blend are the Monoterpenes and Sesquiterpenoids. Diterpenes can also be healing:

Anything you are individually sensitive to should be avoided.

Essential oils with more terpenes and less phenolic compounds might be better tolerated by some people.

The phenolic chemicals could be difficult to break down for someone with certain enzyme or detox dysfunction. More on that later.

I did find that my liver support and detox blends were too rich in clove oil for me to be able to tolerate well. I do have gene differences that slow down my sulfation and methylation pathways and I benefit from taking Dimethylglycine (DMG) as a supplement due to a gene allele that reduces conversion of trimethylglycine (betaine or TMG) into DMG. Phenols can be metabolized or deactivated in a variety of ways, a “sensitive” person might have dysfunction or deficiency affecting several of the methods.

That will be discussed later, first which essential oils might be tolerated by a person who is sensitive to the phenol rich oils?

Terpenes such as Monoterpene, Diterpene and Sesquiterpene have health benefits.

Essential oils with more terpenes and less phenols might be tolerable for someone with salicylate/phenol sensitivity.

They include:

Monoterpenes (one terpene group) in commonly used essential oils:

Pine (alpha-Pinene); Orange - 85-95%, (d-limonene); Galbanum (beta-pinene); Balsam or Silver fir 75-90% (pinenes & l-Limonene); Juniper (Sabinene); Frankincense - 64-90%, (Myrcene); Marjoram (y-Terpinene); Ginger (beta-Phellandrene); Spruce (Camphene); Basil (Ocimene); Galbanum - 50-95%, (d-3-Carene); Thyme (p-Cymene). (page 273, Table 14)
Others: Yarrow - 20-65%, Dill - 35-65%, Angelica - 65-95%, Celery Seed - 70-85%, Elemi - 55-90%, Cannabis - 10-22%. Caraway - 30-65%. Cistus - 42-65%. Eucalyptus - 12-35%. Hyssop - 20-40%. Citrus family oils all have a lot of monoterpenes.

Sesquiterpenes (one and a half terpene groups) found in essential oils:

Fleabane (alpha-Bergamotene); Myrrh - 55-75%, (Bisabolene); White Fir (d-Cardinene); Black Pepper, (beta-Caryophyllene); Blue Tansy (Chamazulene); Rosewood - 1-3% (alpha-Copaene); Ginger (alpha-Curcumene); Helichrysum - 10-20%, (gamma-Curcumene); Elemi - 1-4% (Elemene) *Myrrh/Frankincense family; Valerian (alpha-Farnesene); German Chamomile (beta-Farnesene); Patchouly (Guaiene); Sage (Humulene); Vitex (Longifolene); Celery (alpha-Selenene); Ylang ylang - 39-55%, (alpha-Ylangene). (page 277, Table 15) Also: Yarrow - 25-55%, Celery seed - 6-12%, Carrot seed - 14-18%, Frankincense - 5-10%, Blue Cypress - 10-22%, Cannabis - 41-52%. Caraway - 1-10%. Cedarwood - 55-90%. Eucalyptus - 6-9%. Hyssop - 3-7%.
I love Ylang ylang essential oil for racing heart symptoms that can occur with excess salicylate or sulfates.

Diterpenes (two terpene groups) found in essential oils:

White Camphor - 1-4%, (camphorene and Hishorene); Pine (Cembrene); Cistus - 1-2%, (Labdanenol and Labdanendiol); Cypress (Abienol, Manool, Pimarino, Sempervirol, Totarol, Cupressic Acid); Jasmine (phytol); Clary Sage (Sclareol); Marijuana (Cannabinol). (page 284, Table 16)
*I find Cypress essential oil extremely helpful for migraines or muscle pain - apply to back of neck above the ridge at the hairline where the muscles tend to knot up.

What is going on with phenol/salicylate sensitivity?

Gene differences or nutrient deficiencies or lack of protein might all be factors. Being overly acidic internally would also lead to poor excretion of the phenols or salicylates.

Food sensitivities to the whole group of polyphenols may occur when a person has gene alleles affecting their ability to detoxify benzene rings - but it isn’t well understood. (Skypala, et al., 2015)

According to Brave AI search results - Key Enzymes and Reactions affecting phenol sensitivity include:

Cytochrome P450 (CYP450) enzymes (e.g., CYP1A2, CYP2C9, CYP3A4)
UDP-glucuronosyltransferases (UGT)
Glutathione S-transferases (GST)
Sulfotransferases (SULT)
Glycine N-methyltransferase (GNMT)

… Since glyphosate seems to interfere with CYP enzymes, everyone in the US may have somewhat impaired detoxification of phenolic chemicals.

… a diet low in protein might be low in glycine and cysteine needed to make glutathione or to glycinate with the GNMT enzyme. Polyphenols and other Nrf2 promoters could help by promoting increased glutathione production.

… a diet high in dietary sulfate preservatives or sulfur containing foods might be overloading the sulfation detox pathways which tend to be slow even without dysfunctional gene alleles.

… Someone with impaired bile production or excretion would be excreting through that pathway. *These next points are discussed below.

… Someone with gut dysbiosis might not have beneficial species which help break down phenolic chemicals.

… Someone lacking nutrients needed for the methylation cycles might have impaired methylation even though their enzymes are functional.

The MAO and COMT gene alleles discussed in a recent post affect the deactivation of other chemicals. Mentioned in the last post - Catecholamines (dopamine, norepinephrine, epinephrine) require MAO and COMT enzyme function for deactivation. (Kuhar, et al., 1999) They can be made from the polyphenol catechins by some beneficial species of our gut microbes.

Phenol rich essential oils may cause symptoms of intolerance more easily because of rapid absorption and ease of use as food seasonings.

In order from most concentrated in phenols - Anise tops the list at 90% and I have seen a caution about use of it. Phenol rich oils can be more likely to cause skin sensitivity and should be diluted or used in a diffuser.

As a phenol sensitive person - I do have problems with some of the herbs or oils in the top three rows - cinnamon, thyme, peppermint, oregano, clove and fennel. I generally have not had problems with oils lower on the list - marjoram, ylang ylang, Bay laurel, rose, eucalyptus and myrrh. It is an accumulative issue though, even though myrrh has very little, I have occasionally noticed the ‘salicylate’ symptoms when using myrrh drops in hot beverages.

Is it phenol sensitivity or salicylate sensitivity - and why is that so confusing?

Because it is overlapping issue, both matter. And poor detox or lack of nutrients may vary.

Both phenols and salicylates can accumulate and add to negative symptoms of gassy bloating digestive pain, racing heart, disoriented thinking, congestion/asthma, and swelling of the legs or body.

Standard medical care might diagnosis all that as “indigestion”, “heart disease”, “asthma”, “mental illness or ADHD”, and “leg lymphedema” rather than identifying the actual problem of excessive accumulation of salicylates and phenols. A bunch of medications might be prescribed to the person who is suffering these confusing symptoms, BUT, none of the symptom management drugs would help the actual problem that is due to intake of phenols and salicylates along with a lack of glycine and other nutrients that are needed for the sulfation and methylation pathways to function. The person might be put on a low sodium diet, which if too low, can itself be a cause of lower leg swelling - then the person might try to cut out salt even more, which would just worsen the symptoms of sodium deficiency.

CONFUSING? YES, VERY. I generally don’t get negative symptoms from the oils with less phenol content, but I do have problems with oils or spices on the upper three lines. Tea tree oil topically hasn’t been a problem for me, for occasional use on a small wound. I also use it for dental oil pulling along with clove oil. Adding clove oil to foods or beverages was a problem though.

90-66%: Anise, Tarragon, Clove, Basil, Oregano, Fennel.
55-49%: Mountain Savory, Thyme.
39-25%: Peppermint, Tea Tree, Moroccan Thyme, Citronella, Cinnamon.
18-14%: Marjoram, Nutmeg, Ylang ylang, Calamus, Parsley.
6-3%: Bay Laurel, Eucalyptus dives, Thuja, Cassia, Cumin, Myrtle, Hyssop.
2-1%: Helichrysum, Rose, Eucalyptus, Lemon Eucalyptus, Myrrh.

Brave AI - *slightly edited - Phenol Metabolism in Humans

Phenols, a class of compounds found in various foods and beverages, undergo significant metabolism in humans after ingestion and may have been modified into smaller metabolites by gut microbes during digestion. The metabolic pathways involve multiple enzymes and reactions, ultimately leading to the formation of conjugated metabolites, which are then excreted in urine or released in bile which may be further degraded by the gut microbiota before being excreted in feces.

Phase I Reactions

Cytochrome P450 (CYP450) enzymes: Phenols are initially metabolized by CYP450 enzymes, primarily CYP1A2, CYP2C9, and CYP3A4, in the liver and small intestine. These enzymes catalyze hydroxylation, epoxidation, and dehydrogenation reactions, converting phenols into more polar and reactive metabolites.
Glucuronidation: Some phenolic compounds, such as flavonoids and phenolic acids, are directly glucuronidated by UDP-glucuronosyltransferases (UGT) in the liver and small intestine. This reaction forms glucuronide conjugates, which are more water-soluble and easier to excrete.

Phase II Reactions → slow glutathione production, poor sulfation or lack of glycine could interfere.

Conjugation with glutathione: Reactive metabolites formed in Phase I reactions can react with glutathione (GSH) to form glutathione conjugates. This reaction is catalyzed by glutathione S-transferases (GST).
Sulfation: Phenolic compounds can be sulfated by sulfotransferases (SULT) in the liver and small intestine, forming sulfate conjugates.
Glycination: Some phenolic compounds can be glycinated by glycine N-methyltransferase (GNMT) in the liver, forming glycine conjugates.

Excretion and Gut Microbiota Degradation → gut dysbiosis or gallbladder disease might interfere.

Biliary excretion: Conjugated metabolites are excreted into the bile and eliminated through feces.
Urinary excretion: Some conjugates, such as glucuronides and sulfates, are excreted into the urine.
Gut microbiota degradation: The gut microbiota, particularly bacteria and fungi, can degrade phenolic compounds and their conjugates, producing smaller phenolic acids and aromatic compounds.

(Summary Brave AI/ ) (Bento-Silva, et al., 2020)

Overall metabolic acidosis may increase problems with sulfate excretion. Less is associated with some types of kidney disease. Regular intake of sodium bicarbonate reduced kidney dysfunction in an animal model, and ammonia - sulfate metabolism gone awry, was reduced. (Chen and Abramowitz, 2014) Caution with vitamin B6 supplements if sulfate metabolism is dysfunctional, increased sensitivity to B6 can cause peripheral neuropathy - numbness and tingling in the fingers. Stop the vitamin B6 and work on your sulfur metabolism.

“Nath et al. examined the role of ammonia in the pathogenesis of tubulo-interstitial injury using the rat remnant kidney model [31]. Chronic sodium bicarbonate supplementation lowered renal vein total ammonia concentrations, reduced tubular deposition of complement components C3 and C5b-9, and ameliorated structural and functional evidence of tubulo-interstitial damage.” (Chen and Abramowitz, 2014)

Figure 1. “Structures of Benzoic acid (1), common Hydroxybenzoic acids (2–5) and common Hydroxycinnamic acids (6–10)” 2-5 - hydroxybenzoic acids include Gallic acid, found in pomegranate peel, Protocatechuic acid, p-Hydroxybenzoic acid, and Vanillic acid, found in vanilla. 6-10 - hydroxycinnamic acid derivatives include Cinnamic acid, found in cinnamon, Caffeic acid found in pomegranate peel, coffee, and chocolate, p-Coumaric acid, H, Ferulic acid, and Sinapic acid. (Bento-Silva, et al., 2020)

“Based on their chemical structure, phenolic acids can be classified into benzoic acid and cinnamic acid derivatives (Fig. 1). Hydroxycinnamic acids (HCAs) are synthetized in plants from phenylalanine via cinnamic acid or directly from tyrosine by tyrosine ammonia-lyase, producing the simplest hydroxycinnamic acid, p-coumaric acid, which can be further synthetized into caffeic, ferulic and sinapic acids [1, 2].” (Bento-Silva, et al., 2020)

Reference List

The Chemistry of Essential Oils Made Simple - God’s Love Manifest in Molecules, by David Stewart, PhD, DNM, 2005, Care Publications (Read online, internet archive) But at 906 pages it has a lot of reference tables about essential oils and the phytonutrients they contain, shop around if buying used. Some ebay copies are priced in the $100s, while it is under $15 elsewhere. It would be a collectible within Young Living essential oil fans. (AbeBooks) Post with a review/summary of an interesting chapter: Alchemy - changing lead to gold? or Silica to calcium? (deNutrients.substack)

(Bento-Silva, et al., 2020) Bento-Silva, A., Koistinen, V.M., Mena, P. et al. Factors affecting intake, metabolism and health benefits of phenolic acids: do we understand individual variability?. Eur J Nutr 59, 1275–1293 (2020). https://doi.org/10.1007/s00394-019-01987-6 https://link.springer.com/article/10.1007/s00394-019-01987-6

(Chan, 1996) Chan TY. The risk of severe salicylate poisoning following the ingestion of topical medicaments or aspirin. Postgrad Med J. 1996 Feb;72(844):109-12. doi: 10.1136/pgmj.72.844.109. PMID: 8871462; PMCID: PMC2398362. https://pmc.ncbi.nlm.nih.gov/articles/PMC2398362/

(Chen and Abramowitz, 2014) Chen W, Abramowitz MK. Metabolic acidosis and the progression of chronic kidney disease. BMC Nephrol. 2014 Apr 3;15:55. doi: 10.1186/1471-2369-15-55. PMID: 24708763; PMCID: PMC4233646. https://pmc.ncbi.nlm.nih.gov/articles/PMC4233646/

(Kuhar, et al., 1999) Kuhar MJ, Couceyro PR, Lambert PD. Storage and Release of Catecholamines. In: Siegel GJ, Agranoff BW, Albers RW, et al., editors. Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. Philadelphia: Lippincott-Raven; 1999. Available from: https://www.ncbi.nlm.nih.gov/books/NBK28060/

(Dutta, et al., 2023) Dutta, B.J., Rakshe, P.S., Maurya, N., Chib, S., Singh, S., Unlocking the therapeutic potential of natural stilbene: Exploring pterostilbene as a powerful ally against aging and cognitive decline, Ageing Research Reviews, Vol 92, 2023, 102125, ISSN 1568-1637, https://doi.org/10.1016/j.arr.2023.102125. https://www.sciencedirect.com/science/article/pii/S1568163723002842

(Arora, 2013)

(Durazzo, 2018)

(Bonzanini, et al., 2009) F. Bonzanini, R. Bruni, G. Palla, N. Serlataite, A. Caligiani, Identification and distribution of lignans in Punica granatum L. fruit endocarp, pulp, seeds, wood knots and commercial juices by GC–MS, Food Chemistry, Vol 117, Issue 4, 2009, pp 745-749, ISSN 0308-8146, https://doi.org/10.1016/j.foodchem.2009.04.057. https://www.sciencedirect.com/science/article/pii/S0308814609005160

(Duda-Chodak and Tarko, 2023) Duda-Chodak A, Tarko T. Possible Side Effects of Polyphenols and Their Interactions with Medicines. Molecules. 2023 Mar 10;28(6):2536. doi: 10.3390/molecules28062536. PMID: 36985507; PMCID: PMC10058246. https://pmc.ncbi.nlm.nih.gov/articles/PMC10058246/

(Islam, et al., 2017) Islam T, Yu X, Badwal TS, Xu B. Comparative studies on phenolic profiles, antioxidant capacities and carotenoid contents of red goji berry (Lycium barbarum) and black goji berry (Lycium ruthenicum). Chem Cent J. 2017 Jun 24;11(1):59. doi: 10.1186/s13065-017-0287-z. PMID: 29086843; PMCID: PMC5483215. https://pmc.ncbi.nlm.nih.gov/articles/PMC5483215/

(Dubey, et al., 2024) Roshan Kumar Dubey, Satyam Shukla, Vaishnavi Shukla, Sumit Singh, Sea buckthorn: A potential dietary supplement with multifaceted therapeutic activities, Intelligent Pharmacy, Vol 2, Issue 5, 2024, pp 681-687, ISSN 2949-866X, https://doi.org/10.1016/j.ipha.2023.12.003. https://www.sciencedirect.com/science/article/pii/S2949866X23001296

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