Differences Between Oregano, Sweet Marjoram & Thyme Essential Oils

This article originally appeared in the NAHA Journal (Spring 2019) and it is republished here according to the NAHA Writer Guidelines 2019-20 copyright statement.

By Kathy Sadowski, MS in Aromatherapy, RA (ARC), Professional NAHA and AIA Member, LMT

The plants commonly called oregano (Origanum vulgare), sweet marjoram (Origanum marjorana), and thyme (Thymus vulgaris) have a confusing combination of similarities and differences. For example, there are thyme species with marjoram common names (Thymus mastichina is commonly called Spanish marjoram). Further, marjoram is part of the Origanum (oregano) genus and there are an astonishing variety of chemotypes. With that being said, the most important information to research when identifying a bottle of essential oil from one of these species is its chemistry profile.

Why is the chemistry so important?

Here are some examples.

• There is a marjoram species (O. majorana ct. carvacrol) whose chemistry is more like that of the oregano species (O. vulgare) because it is high in the chemical component of carvacrol.
• A thyme species (T. vulgaris ct. linalool) is very similar to the linalool chemotype of wild marjoram ( O. majorana ct. linalool).
• There arethyme plants (T. vulgaris ct. thymol) that are high in carvacrol and thymol, similar to oregano (O. vulgare). 

Thus, one cannot automatically assume oregano (O. vulgare) and thyme (T. vulgaris) essential oils are “hot” while marjoram (O. marjorana) essential oil is more gentle. These chemo-varieties come with vastly different therapeutic uses, therapeutic margins, and contraindications.

This article will first provide an overview of the plant varieties. Then, it will discuss the importance of knowing the major chemical constituents for a specific essential oil as well as therapeutic uses and contraindications associated with the chemistry of the oil.

Botanical Overview of Plant Varieties

Below is a general overview of oregano, sweet marjoram, and thyme. It is important to know the many variations of these plants.

Oregano (Origanum vulgare) is a perennial herb growing up to thirty inches tall, with opposite spade-shaped leaves about one inch long. Its flower are tiny purple spikes. Dried aerial parts are used to make the essential oil, which is mostly made up of carvacrol, with thymol, and monoterpenes. The aroma is very strongly herbal and not typically used in perfumery.

Sweet Marjoram (Origanum marjorana) is a perennial herb like oregano, with oval-shaped soft hairy leaves about a half inch long. Flowers are tiny white or pink spikes. Dried areal parts are used to make the essential oil. The aroma of this essential oil is camphoraceous, woody, and spicy.

Thyme (Thymus vulgaris) is a bushy evergreen shrub growing up to one foot tall. Its leaves are smaller than oregano and sweet marjoram, with a grey-green color, and tiny pale pink or purple flowers. Arial parts are used to make the essential oil. The essential oil is often rectified, with vast species variations as well. Two key chemotypes of this essential oil are Thymus vulgaris ct.thymol, with a medicinal and herbal aroma, and Thymus vulgaris ct. geraniol,  with a sweet and herbal aroma.

Botanical Variations

In the plant family, Lamiaceae there are over 200 genus, and over 7,000 species. Oregano and sweet marjoram are of the Origanum genera, and thyme is of the Thymus genera. 

Origanum Genus

There are over fifty plant species in the Origanum genus, including sweet marjoram (O. marjorana) and oregano (O. vulgare).

Sweet Marjoram (Origanum marjorana) hasmultiple species with very different chemotypes.

• Sweet marjoram (O. majorana) is typically high in monoterpenes, alcohols, and esters. It has about 30% terpinen-4-ol, plus sabinene, linalyl acetate, terpinenes, cymene, and a small amount of linalool.¹
• Another “sweet” French type of O. marjorana has over 50% 1,8-cineole, up to 12% linalool, with terpenes.²
• Wild marjoram (O. majorana ct.carvacrol) has a type that is very high in carvacrol, with up to 81%.¹
• Wild marjoram (O. majorana ct. linalool) also has type that is very high in linalool (upwards of 66%), and also has a high amount of carvacrol.¹
• A Spanish chemotype (O. majorana ct.1,8-cineole) can contain over 62% 1,8-cineole.²

Oregano hasmultiple species, subspecies, and chemotypes, which are characteristically very high in carvacrol.  Species include:  O. onites, O, vulgare, and O. syriacum.

Thymus Genus

There are over 350 plant species in the Thymus genus, including the most familiar Thymus vulgaris, whichhas multiple chemotypes.

Thymus vulgaris Chemotypes:

• T. vulgaris ct. geraniol, which may commonly be called sweet thyme, can contain up to 80% geranyl acetate and geraniol.²
• T. vulgaris ct. limonene contains mostly thymol, limonene, and carvacrol.¹
• T. vulgaris ct. linalool can contain up to 79% linalool, with a high amount of linalyl acetate.¹
• T. vulgaris ct. carvacrol is high in carvacrol.¹
• T. vulgaris ct. thymol, also called red thyme, is high in thymol.^1,2

Other Thymus Species:

• Thymus mastichina has the confusing common name of Spanish marjoram, even though it is not in the Origanum genus. Its chemistry is about 50% 1,8-cineole, with camphor, alpha pinene, camphene, borneol, beta pinene, and alpha-terpineol.
• Thymus satureioides is high in borneol, carvacrol, beta terpineol, and thymol.
• Commonly called lemon thyme, Thymus citriodorus is high in geraniol, with carvacrol, geranial, neral, and other components.
• Species high in carvacrol and thymol include: T. spicata (spike thyme), T. zygis (often called Spanish thyme), and T. serpyllum, also known as creeping thyme.

Understanding the Chemistry

After reviewing the chemistry associated with the varieties of oregano, sweet marjoram, and thyme, we see certain chemical constituents repeatedly. Here are three key points to consider when looking at the constituents of these three plant essential oils.

• Constituents with a strong therapeutic activity, but a small therapeutic margin, include: Phenols (carvacrol and thymol), ketones including camphor, and the oxide 1,8-cineole.  Essential oils high in these constituents should be avoided with pregnant women, small children, and those with certain medical conditions.³
• Monoterpenes are light in molecular weight and include: Terpinene, limonene, cymene, sabinene, and pinene. These constituents are analgesic, anti-inflammatory, anti-spasmodic, and antimicrobial. Being highly volatile, these constituents are most prone to oxidation; oxidized oils can cause skin irritation.³
• Gentle constituents with a calming, anti-inflammatory, analgesic, anti-spasmodic, and antimicrobial effect include alcohols and esters such as: Linalool, terpinen-4-ol, borneol, geraniol, and geranyl acetate. These less chemically reactive constituents are generally safer to use with most people.³

Phenols: Carvacrol and Thymol

Phenols are very reactive chemical constituents, and thus have a small therapeutic margin, with potential toxicity in excess or when used for prolonged periods. Essential oils high in phenolic constituents should be avoided during pregnancy, with small children, and only used topically in very high dilution ratios. Small amounts can cause skin and mucus membrane irritation. These constituents may also be contra-indicated with multiple medical conditions and may interact with certain medicines.³

Essential oils high in carvacrol and thymol are potent antimicrobials, antioxidants, insecticidal, and have a stimulating effect:

• Carvacrol is an essential oil constituent identified as having one of the strongest antimicrobial actions.⁴ 
• Thymol has also demonstrated antimicrobial activity in multiple studies.⁵ 
• Thymol and carvacrol are two of the strongest antioxidant constituents of 423 tested essential oils.⁶ 
• Thymol has shown insecticidal and repelling action in multiple scientific studies.⁷ 

Ketones: Camphor

Camphor has a small therapeutic margin, that could be toxic in excess. Prolonged usage should also be avoided. It is not appropriate for children, those who are pregnant, and those with certain medical conditions. On the flip side, camphor has demonstrated antimicrobial action in multiple studies, and may help with respiratory complaints and pain:

• In one human study, participants with the common cold who inhaled a mixture of aromatic vapors of eucalyptus, menthol, camphor, experienced improved breathing.⁸   
• Another human study showed a topical cream containing glucosamine sulfate, chondroitin sulfate, and camphor reduced symptoms of arthritis in the knee.⁹  

Oxides: 1,8-cineole

The constituent1,8-cineole can be organ and neurotoxic in excess. It can also be a respiratory irritant. It is not appropriate to use with small children, those who are pregnant, and people with certain medical conditions, such as asthma. 

Benefits of 1,8-cineole are its antimicrobial, insecticidal, anti-inflammatory, and expectorant effect:

• Cineole demonstrated good expectorant activity in a study of 386 patients with respiratory disease in an emergency room.¹⁰  
• Cineole may be effective as an anti-inflammatory and analgesic agent based on an in vivo study showing reduced rat paw inflammation and pain reactions.¹¹  
• Cineole, citral, geraniol, linalool and menthol were tested against a variety of bacteria and fungi, showing a range of antimicrobial activity.¹²

Monoterpenes: Terpinene, Limonene, Cymene, Sabinene, and Pinene

Monoterpenes can be antimicrobial, analgesic, and anti-spasmodic. Being highly volatile, these constituents are most prone to oxidation. Oxidized monoterpene rich essential oils can cause skin irritation.³

Alcohols and Esters: Linalool, Terpinen-4-ol, Borneol, Geraniol, and Geranyl Acetate

Alcohols tend to have a low toxicity rating compared to other chemical constituents and are safer with children and those in fragile health. Esters are similar to alcohols, with a gentle nature, and form when an acid combines with an alcohol. Alcohols and esters tend to have analgesic, anti-spasmodic, anti-inflammatory, and antimicrobial activities.  They are associated with a calming effect, such as with linalool.¹³

What Should I do?

Based on all these chemistry variations, the best thing to do when purchasing and/or using a bottle of sweet marjoram, oregano, or thyme essential oil, is to first review a GC-MS (Gas chromatography–mass spectrometry) report. This should be accessible from reputable essential oil companies.  It is a report that lists the amounts of each chemical constituent found in a batch of essential oil.   This helps you to understand the unique chemistry profile of the specific bottle of essential oil you are buying. A trained nose may also be able to distinguish some key aroma constituents in an essential oil.

Recipes

Oregano Herbal Stuffy Nose Tea

Ingredients

• 10 fresh oregano leaves, or 1/4 tsp of dried oregano (Origanum ssp.)
• 1 tsp. of honey
• 10 oz. of hot water

Instructions for Making and Use:

• Pour hot water over the oregano leaves. Then, allow them to steep for ten minutes.
• Next, strain the leaves. Finally, add honey, and drink as a tea.
• Adult Use Only.  Do not exceed one cup a day. Furthermore, do not drink for a prolonged period exceeding two weeks. Avoid use with small children, with pregnant women, and with certain medical conditions.  It may increase bleeding in those with bleeding disorders. Avoid up to two weeks before surgery.  It might lower blood sugar levels and affect medications related to diabetes.   

Essential Oil Bug Spray Recipe

Ingredients:

• 1 tsp. of dish soap
• 3 oz. witch hazel (Hamamelis virginiana) or vodka
• 4 oz. distilled water
• ½ tsp. of sea salt

Essential Oils:

• 20 drops of sweet marjoram (Origanum majorana) OR thyme (Thymus ssp.)
• 20 drops of Texas cedarwood (Juniperus mexicana) OR juniper berry (Juniperus communis)20 drops of blue gum eucalyptus (Eucalyptus globulus) OR citronella (Cymbopogon nardus)

Instructions for Making and Use:

• First, mix the dish soap, essential oils, and witch hazel or vodka together in an 8 oz. spray bottle. Separately, bring the water and salt to a boil and then simmer until the salt dissolves. Add the cooled salt water to the bottle; shake well. 
• Adult Use Only. Shake the bottle and spray an amount equal to about 1 tsp onto the skin.  Re-apply as needed, and shake the bottle before each use. Avoid eyes and mucous membranes. Discontinue use if irritation occurs Not for prolonged use. Avoid use in pregnancy, with young children, and with certain medical conditions. 

References

1. Tisserand, R. & Young, R.  (2014).  Essential Oil Safety, 2^nd Edition.  Churchill Livingstone, Elsevier.
2. Lis-Balchin, M. (2006). Aromatherapy Science.  A Guide for Healthcare Professionals. Pharmaceutical Press.
3. Bowles, J.  (2003).  The Chemistry of Aromatherapeutic Oils, 3^rd Edition.  Allen & Unwin.
4. Can Baser, K. H. (2008). Biological and pharmacological activities of carvacrol and carvacrol bearing essential oils. Current pharmaceutical design, 14(29), 3106-3119.
5. Solórzano-Santos, F., & Miranda-Novales, M. G. (2012). Essential oils from aromatic herbs as antimicrobial agents. Current opinion in biotechnology, 23(2), 136-141.
6. Anthony, K. P., Deolu‐Sobogun, S. A., & Saleh, M. A. (2012). Comprehensive assessment of antioxidant activity of essential oils. Journal of food science, 77(8), C839-C843.
7. Nerio, L. S., Olivero-Verbel, J., & Stashenko, E. (2010). Repellent activity of essential oils: a review. Bioresource technology, 101(1), 372-378.   
8. Cohen, B. M., & Dressier, W. E. (1982). Acute aromatics inhalation modifies the airways. Effects of the common cold. Respiration, 43(4), 285-293. 
9. Cohen, M., Wolfe, R., Mai, T., & Lewis, D. (2003). A randomized, double blind, placebo controlled trial of a topical cream containing glucosamine sulfate, chondroitin sulfate, and camphor for osteoarthritis of the knee. The Journal of rheumatology, 30(3), 523-528.
10. Li, G. A. O. (1989). The expectorant effect of cineole compositus in 386 patients with respiratory diseases. Chinese Journal of Rehabilitation;1995-03.
11. Santos, F. A., & Rao, V. S. N. (2000). Anti-inflammatory and antinociceptive effects of 1, 8-cineole a terpenoid oxide present in many plant essential oils. Phytotherapy research, 14(4), 240-244.
12. Pattnaik, S., Subramanyam, V. R., Bapaji, M., & Kole, C. R. (1996). Antibacterial and antifungal activity of aromatic constituents of essential oils. Microbios, 89(358), 39-46.
13. Linck, V. M., Da Silva, A. L., Figueiró, M., Caramão, E. B., Moreno, P. R. H., & Elisabetsky, E. (2010). Effects of inhaled Linalool in anxiety, social interaction and aggressive behavior in mice. Phytomedicine, 17(8), 679-683.