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.
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.
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.
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.
Oregano hasmultiple species, subspecies, and chemotypes, which are characteristically very high in carvacrol. Species include: O. onites, O, vulgare, and O. syriacum.
There are over 350 plant species in the Thymus genus, including the most familiar Thymus vulgaris, whichhas multiple chemotypes.
Thymus vulgaris Chemotypes:
Other Thymus Species:
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.
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:
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:
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:
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.
Oregano Herbal Stuffy Nose Tea
Instructions for Making and Use:
Essential Oil Bug Spray Recipe
Instructions for Making and Use: