Here's a quote from the doTERRA website, that I think is telling. I have marked in bold the parts I wish to discuss:
Essential oils have been used throughout recorded history for a wide variety of wellness applications. The Egyptians were some of the first people to use aromatic essential oils extensively in medical practice, beauty treatment, food preparation, and in religious ceremony. Frankincense, sandalwood, myrrh and cinnamon were considered very valuable cargo along caravan trade routes and were sometimes exchanged for gold.
Borrowing from the Egyptians, the Greeks used essential oils in their practices of therapeutic massage and aromatherapy. The Romans also used aromatic oils to promote health and personal hygiene. Influenced by the Greeks and Romans, as well as Chinese and Indian Ayurvedic use of aromatic herbs, the Persians began to refine distillation methods for extracting essential oils from aromatic plants. Essential oil extracts were used throughout the dark ages in Europe for their anti-bacterial and fragrant properties.
In modern times, the powerful healing properties of essential oils were rediscovered in 1937 by a French chemist, Rene-Maurice Gattefosse, who healed a badly burnt hand with pure lavender oil. A French contemporary, Dr. Jean Valnet, used therapeutic-grade essential oils to successfully treat injured soldiers during World War II. Dr. Valnet went on to become a world leader in the development of aromatherapy practices. The modern use of essential oils has continued to grow rapidly as health scientists and medical practitioners continue to research and validate the numerous health and wellness benefits of therapeutic-grade essential oils.I'll describe the errors that I see with these paragraphs in order.
"Essential oils have been used throughout recorded history for a wide variety of wellness applications."The first red flag I saw when I began researching essential oils was the logical fallacy "appeal to antiquity" - that is claiming that something has powerful properties because some ancient civilization used it. doTERRA is no different. The fact that ancient Egyptians used essential oils is irrelevant to the claim at hand - that they serve some medically relevant purpose. We cannot determine whether something is good or bad just because it has ancient origins. Treating disease by ingesting animal feces or applying it to your skin is also an ancient Egyptian remedy, in fact more common than essential oils, but I don't see that catching on in the same way. I'll admit, the appeal to antiquity does sound appealing, but it should; it's a marketing tool.
"Essential oil extracts were used throughout the dark ages in Europe for their anti-bacterial and fragrant properties."There is no way that essential oils were used in Europe during the dark ages for their anti-bacterial properties. The germ theory of medicine was not developed at the time, and was not used clinically until the 1870s. However, let's give them the benefit of the doubt and say that essential oils were used throughout the dark ages in Europe for their anti-bacterial properties. When you think "anti-bacterial" do you really think of the dark ages as a good example? Just think, now you too can have a life expectancy of thirty years!
"French chemist, Rene-Maurice Gattefosse, who healed a badly burnt hand with pure lavender oil."That's right, the whole of the modern argument rests on one piece of anecdotal evidence. It's fine, of course, to mention an anecdote as the reason for pursuing an area of research. The most common example I can think of is Sir Alexander Fleming and the discovery of penicillin. The story of its discovery is famous, but no one says that penicillin works because Fleming noticed that his moldy bread stopped bacterial growth. For the same reason you can't claim that lavender oil heals burnt hands because someone says it worked once. Penicillin is well understood and has plenty of research to support its antibacterial claims. Essential oils? Not so much.
"The modern use of essential oils has continued to grow rapidly as health scientists and medical practitioners continue to research and validate the numerous health and wellness benefits of therapeutic-grade essential oils."This is the most telling sentence of all. Everything before this sentence is full of specific people, times, and places that support the health benefits. The second they bring up modern research, though, they become vague and non-specific. Why not say "in recent years, researchers at Harvard have shown that..." or something like that? The reason is simple. There actually isn't any modern research that supports the claims. Essential oils claim to be effective at treating a wide range of diseases. They are claimed to have antimicrobial, antifungal, antiviral, and antibacterial properties. This is not the case. Only one type of essential oil (tea tree oil) has shown any efficacy, and it has only shown weak antimicrobial and anti-inflamatory properties. No essential oil has shown any antifungal, antiviral, or antibacterial activity in vivo.1
Now, I've carried on about how essential oils are no good for you, but that is not completely true. I began this research open minded, and I'm more than willing to list the good along with the bad. Essential oils are also used for aromatherapy, and the idea behind aromatherapy isn't completely bunk. After all, when I have a cold I use Vick's vapor rub and I feel immediately better. I also think that certain smells can be soothing. Those are two legitimate uses for aromatherapy. If the only claim that proponents of essential oils made was "this smells good, I think you'll enjoy it" I wouldn't be writing this post at all. That's not the case, though. Websites like this one make extraordinary health claims like curing colds, asthma, bronchitis, hypertension, liver congestion, heart palpitations, depression, and boosting your immune system.2 Other websites make fanciful claims like "restore your body's natural energy balance", which are completely meaningless and will be the subject of a later post. Unfortunately, the health claims made have been studied and are just not true.3
Of course, this doesn't mean you can't use essential oils. As with any pseudosciene, I'm of the opinion that you are free to waste your money on whatever you choose. I just wish those selling alternative medicine products were more honest with themselves and their customers.
Am I completely off? Did I miss the point? Please share your thoughts with me on the Facebook page for The Collapsed Wavefunction.
 This may require a little explanation. There are several types of studies, two of which are in vitro (in the glass) and in vivo (in the living). In vitro tests are done by growing bacteria on a small plate, exposing them to something, and seeing if the bacteria survives. In vivo tests are clinical tests done on living subjects. There are many times that an in vitro test gives positive results but do not give the same results in vivo. Essential oils are just one example.
 What does it even mean to "Boost your immune system". That's a story for another day...
 Here are some actual studies, just so you don't think I'm dismissing the claims for no reason.
- Adverse effects of : A systematic review of case reports and case series - This study found that not only are essential oils not helpful, they can be harmful. The most common issues are dermatitis. This is because aromatherapy actually has little to do with smelling anything at all. Most medications are to be applied to your skin. Supposedly they absorb into your skin. Which brings up the question, If aromatherapy has nothing to do with smell and is not suggested as a therapy, why is it called that?
- Effect of sweet orange aroma on experimental anxiety in humans - This sounds promising, right? A nice sweet smell to calm your nerves. Should work, right? This study shows that it actually doesn't
- The effect of aromatherapy on postoperative nausea in women undergoing surgical procedures - This is another one that sounds promising. Aromatherapy to treat nausea. Once again, the study shows that aromatherapy is not helpful.