This is our massive guide to everything you need to know about essential oils. Use the table of contents above to navigate to the section that interests you, or just scroll through the article to learn more about each topic. There are useful lists of oils and tips throughout, so you're sure to find something fascinating. If we missed anything, let us know in the comments and we'll fix it!
Fresh plant material yields about 1-2% by weight of essential oil. [Tisserand, pg 6]. Essential oils can be extracted from many different plants and plant parts including resin, wood, bark, flowers, leaves, fruits, grasses, roots gums, etc. (pg. 8, Tisserand). With this, you can imagine the potency of essential oils.
There are approximately 350,000 plant species and out of those, around 5% (or 17,500) are used for their aromatic qualities. Of this 5%, more than 400 are processed for aromatic uses. Each essential oil can contain anywhere from 20-200 components (constituents).
Although essential oils contain many components that work together, one or two components often dominate their physiological activity.  For example, sweet basil (Ocimum basilicum ct linalool) contains typically 60% linalool while the other components of the oil are usually 5% or less. But there are many things that can affect or change the composition of the chemistry within an essential oil including seasonal variations such as climate change.
The chemical makeup is also dependent on location, soil type, age of the plant, and the time of year it is harvested. A former teacher told us that she always bought her Roman chamomile from the same distiller for years. Always reviewing the GC/MS analysis reports, she noticed a significant difference in the components of the oil. This would change how she would use the oil. When asked why the difference existed, the distiller stated they’d had a flood causing a mudslide which had changed the outcome of the composition of the essential oil.
Lavender (Lavendula angustifolia) is one of the most popular of essential oils. Lavender is an anti-allergenic, immune stimulant, anti-bacterial, anti-inflammatory, anti-spasmodic, healing to our skin (in diluted form), and decongestant. This holds true for almost all essential oils. Although you may have heard they contain vitamins and minerals such as the parent plant, this is not possible. Why? Vitamins are either fat/lipid soluble or water soluble. Since essential oils do not contain water or fat/lipid, they would not be able to ‘hold’ vitamins within them.
However, the therapeutic benefits of essential oils are quite remarkable. Amongst many other properties previously mentioned and dependent on which essential oil, they are also mood enhancers, emotional stabilizers, antispasmodic, aperitive, neurotonic - and the list goes on.
The old adage “a little goes along way” applies to essential oils. These potent oils are effective in tiny doses. The typical, standard usage of essential oils that is considered safe is 2% (or 18 drops to 1 ounce) of a carrier oil or unscented lotion. 2% is very effective.
For acute or chronic issues, we may use up to 5-10% for a short period of time. However, that is dependent on the individual and the individual oil. Some essential oils, such as Thyme (Ct. thymol) are highly irritating and must be diluted at a maximum of 1% for healthy adult skin. We must dilute even more so for young, sensitive, or unhealthy skin. We will discuss safety at length later in this article.
Isolation of Essential Oils
There are several methods used to extract the volatile components of aromatic plants. However, to be a "true" essential oil, it must be either through steam distillation or cold expression. (5)
Historically, plant material was boiled to extract essential oils. This method was called hydro-distillation. Today, a few plants are hydro-distilled. This is the method used for roses. The rose petals are boiled rather than steam distilled.
However, steam distillation is now the preferred method of distillation. This method involves raw plant material, generally chopped into the distillation chamber. At high pressure, the steam is then forced into the holding chamber where the plant material is and, as it passes through, the steam bursts the sacs and cavities of the plant. The volatile constituents within the plant are vaporized and, upon cooling, they do not attain homogeneity with the water so the oil floats on the surface. The oil and water are separated.
The oil product is a mixture of biologically active compounds, producing many beautiful aromatic and therapeutically effective essential oils. The water left behind is referred to as hydrosol; gentle to the skin and preferred for infants and those with sensitive skin.
There are various other methods of distillation as well. For example, Enfleurage, Solvent Extraction, and CO2 Hypercritical Extraction methods are used for Absolutes and CO2 Extracts. Absolutes are extracted in a complex manner that requires the use of chemical solvents that are later removed during the final stages of production. A trace amount of the solvent, however, can remain in the final aromatic absolute. 
Like essential oils, absolutes are highly aromatic liquids extracted from plants. Although the amount of remaining solvent is considered tiny in carefully extracted absolutes, those that practice holistic aromatherapy prefer steam distilled essential oils.
Cold Pressed or Expressed Oils
Citrus oils are either steam distilled or extracted through cold pressed (expression) of the peeling of the fruit. Through cold expression, the larger molecules of concern that cause phototoxicity pass through. This is not always the case though.
Sweet orange does not have phototoxicity concerns. Some citrus plants produce more than oil from the fruit. For example, petitgrain (bigarade - Citrus aurantium var. amara or Bigaradia) is made from the leaves of the bitter orange tree and neroli from the flowers of the tree.
Aromatic botanicals are made of chemical families and within those chemical families are chemical constituents. The composition of some botanicals' constituents is too heavy to be effectively distilled. Solvent extraction methods are often used in these cases.
Absolutes are produced from concretes. A concrete contains both fragrant molecules and plant waxes. The plant material is washed with a nonpolar solvent. An example of this is hexane. (9) Chemical solvents are used in a complex process to produce absolutes.
These solvents are removed later, although trace amounts can remain in the absolute. There are over 350 absolutes. (10) As a rule, absolutes are normally much more potent than essential oils, which means that a little goes a long way.
They have their uses but for this reason, the more holistic approach prefers essential oils. Having said that, absolutes do hold their place within aromatherapy and natural fragrance applications. Just as with steam distilled essential oils, absolutes should be used cautiously and with knowledge. Obviously if one was practicing internal use, the preference would be essential oils since one wouldn’t want to use an oil internally that contains trace amounts of solvents. Although absolutes are not recommended for internal use, they still have excellent therapeutic uses.
Essential Oil Categorization
There are a few ways we can categorize essential oils. Here we’ve listed the plant parts used for essential oils. This is not an all-inclusive list nor does it specify chemo types or species, which is relevant to the safety of each oil. This is to give a general idea what parts of a plant are used for essential oils.
Plant Parts Used
Rind of the Fruit:
Notes (Evaporation Rates) of Essential Oils
Another way to categorize your oils is by "note," which is determined by the evaporation rate of the oil.
The first smell from a blend and the first to evaporate is your essential oils with the top note. The top note fragrance is usually lighter with a beautiful fresh aroma. These oils add brightness to your blend. Some examples of top notes are distilled lime, bergamot, lavender, eucalyptus, grapefruit, and orange.
The next note is the "heart" note, better known as the middle note. It gives blends an aromatic softness and fullness to their overall aroma. Some middle notes can be top-middle or middle-base, meaning they have notes of the top or base aromas within them. They absolutely harmonize your blend as you will notice when you learn the middle notes. These oils are your mentally and physically calming and soothing oils. Great middle notes include Roman chamomile, lavender, ravintsara, rosewood, clary sage, ylang ylang, jasmine, and many more.
Last is the base note. These are the oils that provide that deep, warm, and grounding quality to your blend. They function as fixatives by reducing the evaporation rate of the top notes. Base notes add a deepness to the blend and more often than not they have beautiful, deep, and earthy aromas. Because of their calming and grounding qualities, base notes are your relievers of stress, anxiety, and insomnia.
Several of the essential oils derived from woods, resins, and roots are base notes. Ylang ylang is an exception. It is a base-middle note and falls under both categories. It’s derived from the tree's beautiful, white, fragranced flower. Base notes are so soothing and harmonizing for the mind and body. Some great base notes include cedarwood, patchouli, vetiver and myrrh.
When blending top, middle, and base notes, your overall aroma will change over time as the evaporation takes place. You may pick up the citrus aroma at first then later it may be the middle notes that stand out. It is remarkable how the aroma changes, yet still has the lingering scent of the top notes. (12)
So how do we blend these notes? Oils in the same category tend to blend well together. Florals blend well with spicy, citrusy, and woodsy oils. Woodsy oils generally blend well with all categories. Spicy and oriental oils blend well with florals, oriental, and citrus oils. Be careful not to overpower the blend with the spicy or oriental oils.
Minty oils blend well with citrus, woodsy, herbaceous, and earthy.
Essential oils can be categorized into broad groups based on their aromas. An example categorical system is as follows:
- Citrus - Grapefruit, Lemon, Lime, Mandarin, Orange
- Earthy - Oakmoss, Patchouli, Vetiver
- Floral - Chamomile, Jasmine, Lavender, Neroli
- Herbaceous - Basil, Plai, Rock Rose, Rosalina, Rosemary, Sweet Marjoram
- Medicinal/Camphorous - Cajuput, Engelmann Spruce, Eucalyptus, Pinion (Pinyon) Pine, Tea Tree
- Minty - Peppermint, Spearmint, Tulsi, Wintergreen
- Oriental - Ginger, Patchouli
- Spicy - Clove, Cinnamon, Nutmeg
- Woodsy - Cedars, Fir, Pine, Spruce
Applications of Essential Oils
There are many diffusers available these days that are specially made for essential oils, from units designed for homes, cars and even ones you wear. Diffusion works by distributing essential oil molecules through the air. Once in the air, they are inhaled and come into contact with nerves that send them directly to the brain. This is a quick and safe way of letting the essential oils go to work for you.
An alternative to the use of a diffuser is direct inhalation. Inhalation plays a huge role in aromatherapy and presents a very low risk to most people. During inhalation, odor molecules travel through the nose and affect the brain through a variety of receptor sites, one being the limbic system, which commonly is referred to as the emotional brain.
The limbic system is directly connected to those parts of the brain that control heart rate, blood pressure, breathing, memory, stress levels, and hormone balance (Higley & Higley, 1998). This relationship helps explain why smells often trigger emotions. With this information we can hypothesize how inhaling essential oils can have some very profound physiological and psychological effects. Also while inhaling, the oils pass down the trachea into the bronchi, and down to the lungs. More details on this process can be found in Tisserand and Young, Essential Oil Safety, 2nd edition, page 49.
After essential oils reach the bloodstream, they enter the central nervous system (CNS) quite easily. With this being the case, it’s imperative that we safely use essential oils. This easy access to the CNS can pose serious issues and complications when essential oils with cautionary concerns are ignored, especially when it comes to our children.
On diffusion and children, Tisserand states, “A few drops of essential oil in a burner, vaporizer, or in a steam inhalation is virtually risk-free. However, prolonged inhalation (more than about 30 minutes) of concentrated essential oils vapors (e.g. steam inhalation, or direct from a bottle) can lead to headaches, vertigo, nausea, and lethargy. In certain instances, serious symptoms might be experienced, such as incoherence and double vision."
Tisserand continues, "For children of 5 years old or less, direct inhalation should be avoided. Direct inhalation includes inhaling essential oils from the hands, a cotton ball, a nasal inhaler, a bowl of hot water, or similar. Indirect, or ambient inhalation, is safe for young children, and includes any method that vaporizes essential oils into the air.” (13)
Diffusion is safe when we follow some safety guidelines. Diffuse essential oils for no more than 30-60 minute intervals with a 10-minute break. Although this is a safe method of application, when diffusing for children we should still take into consideration the age (do not diffuse around premature infants), the health (especially presence of asthma), the child's weight, and any medications involved. The diffusion method doesn’t erase the importance of any individual oil safety precautions. Some essential oils, no matter what method, are not safe for children so please seek advice from a reputable source on essential oil safety. (14)
I’ve worked my way through Tisserand and Young’s 2nd edition of Safety of Essential Oils book; the one book I refer to when it comes to safety for children. If you purchase this book, I encourage you to read through it before any diffusing. Not one section, chapter, or page will have all the information that is needed to accurately and safely use your essential oils in one convenient place. Research is key.
I asked the author for a more definitive answer on diffusion with children. From Robert Tisserand: "I think after 3 months is OK, so long as diffusion is not too intensive. I know that's vague, but air concentration of volatiles is hard to pin down, and even if we could - there's no clear guideline." Inhalers would fall under “direct inhalation” and should be avoided for those 5 and under. With safety in mind and since each child is an individual with their own weight, health, and age, apply your Mommy instincts for your own child/children. I always recommend looking for scientific based research as listed below.
The most important aspect of essential oils is how to use them safely, especially with children. Because of this, we will concentrate on children when it comes to dermal dosing. Adult dosing can be derived based on the chart below.
Once again, apply your Mommy instincts. Always look up individual safety guidelines for each essential oil as some are not meant to be used topically on children.
Be especially aware that a great deal of caution should be used with topical application on infants since their skin does not mature until around three months. Infant’s skin is not only more sensitive to essential oils, the absorption rate is higher because the skin is more permeable. Premature infants should always be excluded from any amount of dermal use.
Bathing children with essential oils requires a great deal of discretion, however it can be done safely. Use 1 ounce of a water-soluble medium to blend with (jojoba oil is a favorite for this purpose) and 9 drops of lavender (Lavandula angustifolia). Add no more than ½-1 tablespoon to bath, depending on how full you run the bath. Then your little one can enjoy a relaxing bath before nighty-night time.
Lavender serves so many purposes and it really is a perfect essential oil for children. However, even with lavender, it’s still important to do a skin patch test since there has been noted an occasion of irritation from lavender. With multiple therapeutic properties including anti-inflammatory, anti-bacterial, analgesic, sedative, respiratory support and more, this is my go to for children.
For topical use, Tisserand suggests the following:
“Age-related recommended and maximum concentrations of essential oils for massage”
Up to 3 Months
15 + years
Tisserand states that these concentrations aren’t researched based. These are, however, safety suggestions from one of the top experts in the industry. (15)
In both children and adults, different factors can affect the absorption of essential oils through the skin. Warming the area up first with either a warm cloth (if wet, dry thoroughly) or heating pad, then massage the area, will increase the circulation to that area which in turn will allow more absorption of the essential oils.
As to how much is absorbed into the body is determined by several factors. First how much is used and the total dilution rate. The next thing to consider is how they are dispersed, what is the overall area of the body being applied to, the health of the skin and the age of your client. As mentioned above, the temperature also affects the absorption and this can increase by adding a warm cover over the skin after oils are applied. And of course, what essential oils you choose affects the final outcome.
You can find other useful information and guidance at NAHA (National Association for Holistic Aromatherapy) at http://naha.org.
Internal Use of Essential Oils
Internal use of essential oils has become more and more frequent by the untrained, adding to the mound of injury reports. We avoid discussing the topic, sending our readers off with "do not ingest," or "consult a trained Clinical Aromatherapist, one trained in aromatic medicine," or other direction or reason to avoid the discussion of ingesting.
Some, like myself, have studied for years, come from a medical background, and have an understanding of ingestion but, because we are not formally trained, we don't speak of ingesting. So what are people doing? They will seek out answers, whether it is through MLM companies and reps, their friends, or what they can find on the internet.
People either then ingest privately or they are very public about it, encouraging others to follow suit, with no knowledge of the chemistry of good and bad components within essential oils. Most of what we hear and read about ingesting essential oils from the untrained is wrong, unsafe, and dangerous.
There are both harmful and protective therapeutic chemicals within oils. How harmful depends on the individual oil and the person. The “one shoe fits all” scenario does not apply. To avoid risk of a toxic reaction, you need to know the susceptibility of an individual.
To understand the susceptibility, you need to know the age, body weight, health (including those with chronic illnesses or pregnancy), blood pressure, and medications related to the individual. Even hereditary traits should be taken into consideration. There are many essential oils that are never used internally due to concern of either toxicity or mucous membrane damage.
Many components (constituents) within some oils are mucous membrane irritants and, whether delivered in the proper dosing vehicle or not, or in large doses, the essential oil can become unsafe rather than having a healing effect. Large doses brings risk of irritation to your gastric tract or any mucous membranes they come into contact with. Some oils contain components that can affect blood coagulation, some exert hypoglycemic effects, etc.
Armed with proper training, many oils are quite safe taken internally. A part of that training is essential oil pharmacokinetics and pharmacodynamics. To learn more on ingestion, you can visit my website. (16)
Chemistry of Essential Oils
Essential oils consist of many organic molecules made of hydrogen as well as carbon and some oxygen, dependent on the essential oil. Essential oil molecules are made of chemical families such as monoterpenes, monoterpenols, sesquiterpenes, sesquiterpenols, oxides, aldehydes, esters, ethers, ketones, and phenols. It is within these chemical families that you find the components. There can be one or more chemical family within each oil.
What makes each essential oil unique is the constituents. Some constituents found in essential oils