So I'm currently taking a course in essential oil chemistry and it has been fascinating! Now I am a Naturopath not a chemistry major. Most of what I know about chemistry is self-taught so much of this stuff is a bit over my head. So I'm going to try and pass along some of the basics of what I do understand so you can learn too.
The only way to make an essential oil is through steam distillation unless it is a citrus oil, which is cold-pressed from the rind. If any chemical is used to extract the chemical properties out of plant material then it should not be called an essential oil. This is the case in extracts called absolutes. An absolute is made by adding a solvent such as hexane to plant material (biomass) to extract chemical constituents. After the hexane is evaporated you are left with something called the “concrete”. Another chemical, typically ethanol, is added to the concrete and then evaporated and you are left with the absolute and a byproduct of floral wax that is often used for cosmetics and candle-making.
Jasmine is a commonly made absolute. In fact, there is no such thing as a jasmine essential oil commercially because the chemical properties cannot be steam distilled. So if you see jasmine labeled as an essential oil... it's not. Now most of the hexane and ethanol has been evaporated off although there may be trace amounts left in the absolute which should be non-toxic. Absolutes have very different chemical properties compared to essential oils. For example, rose essential oil has almost no color to it but rose absolute is red like the flower and has a subtly different odor and very different chemical profile. You can also extract chemicals using liquid carbon dioxide. These are appropriately called CO2 extracts and they would have therapeutic uses closer to that of the original herb.
Speaking of chemical profiles. All essential oils are made up of chemicals, mostly terpenes, aldehydes, alcohols and hydrocarbons. So if you look up the chemical profile of say, a lemon essential oil from Brazil, you will see that it is 67% limonene, 15% beta-pinene, 5% gamma-Terpinene, 3.55% alpha-Pinene, and the rest minor components of less than 2%. The profile would be different depending on the source. Anything labeled as a fragrance or perfume has a synthetic chemical makeup which means they created those same chemicals in a lab rather than getting them from the natural source. Synthetic fragrances can never match the complexity of an essential oil although much of the perfume and cosmetics industry centers around them.
If you want to know whether you are getting a quality essential oil, the producer should be able to provide you with the chemical analysis. You could then compare this chemical analysis with a database such as Essential Oil University's (www.essentialoils.org). This is a free database although you do have to register to be able to log-in. It will give you some of the standards you can expect from that particular essential oil. You should also be able to find out what the country of origin is for the essential oil and the botanical name. If your essential oil supplier can't tell you any of this information, you might want to look elsewhere.
The essential oils we carry here at Elder & Sage are as high quality as I could find with as much transparency as possible. We have the botanical name and country of origin information readily available and I can provide the chemical analysis on request although it might take me a little work to get it. There are hundreds of essential oils available and I don't have it all printed out at this time.
Once you know the chemical profile you can find out a little bit about the therapeutic value of the essential oil. Careful though, there is a lot of misinformation on the internet and I've found a lot of what is said about essential oils applies more to the herb than the essential oil.
For example, Palmarosa is an essential oil steam distilled from a grass variety. It's main chemical constituent is called geraniol (up to 90%). If you look up Palmarosa essential oil on the internet you may find claims that it is antimicrobial, antiseptic and stimulating to the digestive tract. But if you look up geraniol on PubChem (where I do a lot of my research on essential oil constituents) you won't find any research on these properties. That's not to say it doesn't have those properties, maybe there is anecdotal or clinical evidence to prove it, I'm not sure. But what is exciting about geraniol and Palmarosa is the research that shows it inhibits tumor growth in breast cancer and colon cancer! Geraniol is also found in other essential oils such as geranium and rose.
Now, remembering that essential oils are made up of chemicals is important if we want to talk about the safety of essential oils. Those chemicals are absorbed into the body through inhalation (smelling and breathing), through the skin, and through ingesting them. Depending on the essential oil and the chemical make-up some are perfectly safe and others are not. Some can be toxic, cause skin irritation or respiratory irritation. Too much applied to the body can overwhelm the liver's detox pathways. Ingesting oils is probably the most risky and you should use extreme caution. If you don't understand what's in the oil and what it does in the body then be careful. There are a lot of popular articles out there that say essential oils are natural and perfectly safe even in large amounts but just a quick look on PubChem for some of the most common constituents will tell you otherwise. I'm not trying to scare you off of them but I do think we need to use caution. One to two drops go a long way.
If you are a natural health professional recommending essential oils to your clients then I recommend getting the book on Essential Oil Safety by Robert Tisserand. It's a bit technical for the average user but it would be a great reference book for the practitioner.
Okay, that's enough for today! This is just the tip of the iceberg on essential oils, I could go on and on.
To Your Health!