Synergism in essential oils and aromatherapy

Synergism in essential oils and aromatherapy

by Jade Shutes

Many herbalists acknowledge that one of the main differences between whole herbs and traditional extracts on the one hand, versus individual vitamins, minerals, isolated phytochemicals, or conventional single – molecule drugs on the other hand, is the principle of synergy.

Synergy can be defined in a number of ways, but the underlying idea is that complex interactions among the many constituents of an herb give rise to its unique characteristics, personality, and healing properties. To borrow a concept from physics, the very complexity of a living plant – which contains perhaps thousands of interacting chemicals – gives rise to emergent behavior: activities and effects which could not have been predicted from what is known about the individual components of the system. In other words, the whole herb is far more than the sum of its constituents.   – Lisa Ganora  ‘Herbal Constituents’

If we stop to consider the plants from which we extract essential oils from, we come to the realization that a plant contains ‘a myriad of compounds that work synergistically to protect the plant from harm and carry out all the processes of its metabolism’. The plant does not isolate one constituent over another but rather utilizes its symphony of constituents to create its own intelligence, primal essence, and personality.

The exploration of essential oils by science is often the exploration of isolated compounds rather than whole essential oils. Harris, R. (2002) writes “currently there is an increasing trend towards identifying, isolating and using a single agent, drug, herb or essential oil to exert a specific and focused effect”. A core reason for this is that complex mixtures of compounds are difficult to evaluate scientifically.

Aromatherapists, on the other hand, believe that by working with whole, authentic, unrefined/unaltered essential oils, a greater therapeutic activity is achieved versus utilizing individual isolated components or adulterated/synthetic essential oils. Aromatherapists also believe that utilizing blends or combinations of essential oils designed for a specific purpose enhances the therapeutic efficacy of the end product and indeed that a combination of essential oils are synergistic.

“The holistic perspective begins with the observation that the ‘sum is greater than the parts.’ Thus, the whole organism acts with an intelligence and direction that govern the parts.

The medicinal plant, unlike the drug, constitutes such a ‘whole organism’. The unique slurry of chemicals constitutes is the material expression, so to speak, of an intelligent being that has learned to survive in a challenging niche in the natural environment. It has been ‘standardized’ by Nature, and hardly needs to be tweaked by nosy human beings who think Nature is insufficient to the challenge.” Matthew Wood in The Earthwise Herbal


Synergistic, additive or antagonistic?

The concept of synergy is an important and valuable concept in aromatherapy. Synergism implies that the therapeutic benefit of a mixture of essential oils will be greater than the arithmetical sum of the actions of the mixtures parts. This could be understood as: 2 + 2 = 8. Synergism is observed when the effect of the combined substances is greater than the sum of the individual parts.

Before continuing with our discussion on synergy it is important to note that at times the combination of certain chemical components or essential oils can also have additive or antagonistic effects. An additive effect is observed when the combined effect is equal to the sum of the individual parts (1+2=3) An antagonistic effect is observed when the effect of one or both compounds is less when they are applied together than when individually applied (2+2=3). (1)

In the examples provided throughout the remaining discussion, synergy, antagonistic and additive effects will be briefly covered. Harris (2002) further elucidates that the concept of synergy can occur in aromatherapy via several possibilities. These possibilities include:

1. Synergy within the essential oil itself: This concept means that within a given essential oil, synergy occurs between major and minor constituents or between major components that act together to significantly increase the whole oil’s activity.

Lemongrass Cymbopogon citratus

Cymbopogon citratus

An example of this can be found in research by Onawunmi, et. al. on the “Antibacterial constituents in the essential oil of Cymbopogon citratus”. Cymbopogon citratus (DC.) Stapf., commonly known as lemon grass and used, over many years, for medicinal purposes in West Africa, produces a volatile oil on steam extraction of its leaves. The antibacterial properties of the essential oil have been studied. These activities are shown in two of the three main components of the oil identified through chromatographic and mass spectrometric methods. While the alpha-citral (geranial) and beta-citral (neral) components individually elicit antibacterial action on gram-negative and gram-positive organisms, the third component, myrcene, did not show observable antibacterial activity on its own. However, myrcene provided enhanced activities when mixed with either of the other two main components identified.(2)

2. Synergy between essential oils in a blend: This concept means that by combining two or more essential oils together, the aromatherapist creates a blend or product that is more effective than using only a single essential oil.

This category can reflect two potential pathways on synergism. These pathways include: synergy by therapeutic properties (e.g. an antispasmodic essential oil combined with another antispasmodic essential oil creates highly antispasmodic product) or synergy by chemical components (e.g. an essential oil rich in thymol and an essential oil rich in eugenol will create a highly effective antimicrobial product).

An example of essential oils enhancing the therapeutic property of each other is found in the combination of peppermint with caraway which is currently being marketed for relief of irritable bowel and dyspepsia. According to Harris, the authors of the study suggest that the spasmoyltic effects of caraway are enhanced by the spasmolytic effects of peppermint.

In a research paper on the antimicrobial activity of clove and rosemary oils, clove and rosemary were both shown to exhibit antimicrobial activity against a range of bacteria and fungi. A combination of clove and rosemary exerted additive antimicrobial effects against several strains of bacteria, a synergistic effect against Candida albicans but an antagonistic effect against Aspergillus niger. The authors concluded that this study may be useful for the combination of clove and rosemary essential oils for specific microorganisms in medicine and the food industry.(3)

Another research paper entitled “The anti-microbial efficacy of plant essential oil combinations and interactions with food ingredients” found that in many cases the result was an “additive effect”. The objective of the study was to evaluate the efficacy of plant essential oils in combination and to investigate the effect of food ingredients on their efficacy. The essential oils assessed in combination included basil (Ocimum basilicum), lemon balm (Melissa officinalis), marjoram (Origanum marjorana), oregano (Origanum vulgare), rosemary (Rosmarinus officinalis), sage (Salvia triloba), and thyme (Thymus vulgaris). All the oregano combinations were additive against B. cereus. The following EO combinations also showed additive effects: oregano in combination with basil or thyme against E. coli and P. aeruginosa, oregano combined with marjoram against E. coli, and marjoram and thyme mixed with basil, rosemary or sage against L. monocytogenes. These results can be explained considering the efficacy of the main component.(4)

The German Commission E is a great reference on approved combinations of essential oils mostly for gastrointestinal complaints.  These approved combinations have ‘met a vigorous set of criteria that include evidence of synergistic effects as well as evidence of the improved safety of the product, either by reducing the doe due to synergy or by negating or lessening potential side effects’. (Harris)

Some examples of approved combinations include:

1. Fixed Combinations of Anise oil, Fennel oil, and Caraway oil for Dyspeptic discomfort, especially with mild spasms of the gastrointestinal region, flatulence, and a sensation of fullness.

2. Fixed Combinations of Caraway oil and Fennel oil for Dyspeptic discomfort, especially with mild spasms in the gastrointestinal region, flatulence, and a sensation of fullness.

3. Fixed Combinations of Eucalyptus oil and Pine Needle oil for inhalation and external application in case of illnesses of the respiratory tract caused by a cold.

4. Fixed Combinations of Peppermint oil, Caraway oil, and Fennel oil for Dyspeptic discomfort, especially with mild spasms in the gastrointestinal region, flatulence, sensation of fullness.

(Reference: German Commission E at -

As aromatherapists, we choose a combination of essential oils for a variety of reasons. For instance: in making a remedy for insomnia we would first explore the potential reasons for the insomnia and understand how the insomnia is manifesting in the individual. We may find that the individual is currently feeling ungrounded, scattered, overwhelmed. We can choose essential oils that are sedative (lavender, Roman chamomile) and also choose essential oils that can provide a sense of rootedness and strength. Such oils representing this quality are found in vetiver, cedarwood, and jatamansi. So our final blend could look something like: Lavender, Roman chamomile and Vetiver. This is synergy in action.

Another form of synergistic blending of essential oils can be seen in choosing essential oils based upon their chemistry and ability to mutually enhance one another. An example could look like:

Example of a blend designed for Chronic bronchitis and lowered immunity:

  • Eucalyptus (Eucalyptus globulus): Rich in the oxide, 1,8 cineole. Expectorant and
    respiratory stimulant
  • Rosemary ct. camphor (Rosmarinus officinalis): Rich in camphor and 1,8 cineole. General expectorant and strong mucolytic activity
  • Peppermint (Mentha x piperita): Rich in the alcohol, menthol and ketone, menthone. Opens up airways and enhances immune system
  • Thyme ct. thymol (Thymus vulgaris): Rich in phenol, thymol. Supports and enhances immune system and exerts antimicrobial activity.

There are so many creative ways to utilize this idea of synergy through the combination of essential oils, experiment, enjoy, take notes, and get feedback from your clients, your family and yourself.

It may serve us to remember that essential oils are unique because they are able to affect us on all the levels of our being: mental, emotional, physical, spiritual, and energetic and that their wide range of benefits cannot always be reduced to their chemical components. Schnaubelt (2000) reminds us that aromatherapy is unique in and of itself and that “the more aromatherapy strives to be accepted by the medical profession, the more likely it is to copy its mistakes and failures”.


Aloe vera gel

Aloe vera gel

3. Synergy between essential oils and the base or carrier product
Aromatherapy products designed to be applied to the skin are most often placed in a carrier of some kind. This carrier can include: lotions, gels, creams, vegetable/nut/seed oils, salt, milk, honey, etc. When I was trained in aromatherapy by my mentor, Jan Kusmirek, he taught me that the base or carrier we placed our essential oils was just as important as the essential oils themselves. The idea was that by creating a therapeutic base, we could enhance the overall effectiveness of the blend/product.

Some research is supporting this idea that our carrier base can play a synergistic or antagonistic role. One such study showed that Ocimum gratissimum combined with aloe vera gel has greater therapeutic efficacy against acne conditions then either of the substances used alone. The study found that a 2% concentration of Ocimum gratissimum in 50% aloe vera gel aqueous dilution was optimal and that continuous treatment for not less than 7 days was recommended for the effective treatment of Acne vulgaris.(5)

Another study revealed the synergistic activity of German chamomile and aloe vera gel on delivering moisture to the skin. The study researched three essential oils: mandarin, German chamomile, and orange placed in a aqueous gel. The German chamomile gel provided greater hydration and a longer lasting effect when compared with the control and the other two essential oils. (6)

The combination of honey with a 2% dilution of the leaf essential oil of Ocimum gratissimum showed remarkable antibacterial activity which suggest that formulation of ocimum oil in honey could be invaluable as a topical antiseptic agent for wounds.

The use of an ointment inactivated Ocimum gratissimum’s antibacterial activity. (7)

When blending essential oils into a base product it is valuable to consider what your intention and desired result and how you may utilize base material to enhance the overall effectiveness of your essential oil blend. For instance, I could make a massage oil for aches and pains in the neck and shoulder area using just jojoba and a 10% dilution of essential oils including: birch (Betula lenta), peppermint (Mentha x piperita) and laurel (Laurus nobilis). Taking this a synergistic step further: instead of using jojoba I could create a therapeutic gel to hold the essential oils. Using a concentrated aloe vera gelly I could add Lavender and Roman chamomile hydrosols, St. Johns wort and Arnica herbal infusions, and then the 10% dilution of essential oils. This new blend has increased effectiveness due to the use of a number of products all enhancing one another and the overall purpose of the product.

The concept of synergy is of great value to the aromatherapist in understanding which essential oils to put together for a common purpose as well as why. With the above in mind, here are some tips for maximizing synergy potential when blending:

1. Have a purpose and focus for your blend: avoid trying to achieve too many goals with one formulation.

2. Select essential oils that complement one another: therapeutically, chemically, energetically, and/or aromatically.

3. Use 3-5 essential oils in a formulation to avoid diluting down purpose/focus or using a given essential oil below therapeutic levels.

4. When blending from a clinical framework: focus on either families or components and insure essential oils complement goal.

5. Your base is an important part of your formulation. Choose your base to complement the therapeutic goals of your essential oils synergy. E.g. for dermal inflammation you may choose to blend into a base of calendula herbal oil with tamanu. Or a gel to enhance the cooling sensation of anti-inflammatory essential oils.

6. Know what dosage to use! Acute conditions tend to require higher dosages then chronic conditions or emotional conditions.

For us as aromatherapists perhaps the most important aspect of maximizing synergy potential is our knowledge of and experience with each individual essential oil in our collection. There is not scientific evidence to support all our ideas or creations nor is this important to validate our ability to blend dynamic and highly effective blends/products. With our knowledge and experience, using the framework above and gaining feedback from our clients, we can feel confident in creating aromatherapeutic products.

“Modern Science and medicine are reductionist; that is to say, they reduce phenomena to their smallest pieces to gain understanding. This perspective ignores the possibility that there is a unified being, consciousness, identity pattern, or functional whole at the base of a human, animal, plant, or disease organism. Holism, in contrast, concerns itself with this underlying, unifying entity. – Matthew Wood “The Earthwise Herbal: A complete guide to New World medicinal plants”


Harris, R. (2002). Synergism in the essential oil world. The International Journal of Aromatherapy,12(4), 179-185.
Schnaubelt, K. (2000). Functional Group Therapy. International Journal of Aromatherapy. 10(1/2):62-63.

1. Davidson, PM & Parish, ME. (1989). Methods for testing the efficacy of food antimicrobials. Food Technology, 43(1),148-155.
2. Onawunmi, GO, Yisak WA, Ogunlana EO. (1984). Antibacterial constituents in the essential oil of Cymbopogon citratus. J. Ethnopharmacol. Dec;12(3):279-86.
3. Fu, Y., Zu, Y, Chen, L, et al. 2007. Antimicrobial Activity of Clove and Rosemary Essential oils alone and in combination. Wiley InterScience DOI:10.1002/ptr.2179.
4. Gutierrez, Jorge and Barry-Ryan, Catherine and Bourke, Paula: The anti-microbial efficacy of plant essential oil combinations and interactions with food ingredients. International Journal of Food Microbiology, Vol, 124, Issue 1, 10 May 2008, Pages 91-97.
5. Orafidiya LO, Agbani EO, et. al. (2004) The effect of aloe vera gel on the anti-acne properties of the essential oil of Ocimum gratissium Linn leaf – a preliminary clinical investigation. The International Journal of Aromatherapy 14,15-21.
6. Monges, P, et al. (1994). Comparative in vivo study of the moisturizing properties of three gels containing essential oils: mandarin, german chamomile and orange. Nouv. Dermatol. 13:470-475.
7. Orafidiya LO, Oyedele AO, Shittu AO et al. The formulation of an effective topical antibacterial product containing Ocimum gratissimum leaf essential oil. Int J Aromatherapy. 2002; 12(1): 16±21.