You’ve probably heard of essential oils. They are commonly used in aroma therapy, but some people also recommend that essential oils be applied topically (to your skin) or ingested (alone or used as ingredients in food). What exactly is an essential oil, are they good for you, and are they safe? Here’s the skinny.

What is an essential oil?

An essential oil is an extract from a plant. Specifically, it is a mix of volatile chemicals (chemicals with a low boiling point) that are extracted using distillation or solvents. The term “essential” in this case refers to the “essence” of the plant in question – a nod to that fact that essential oils from a given plant generally smell and/or taste like that plant. The essential oils from citrus fruit, for instance are generally very citrusy (which is a real word). “Essential” in this context does not mean that these oils are essential for life or good nutrition – you do not need essential oils in your diet. They are called oils because they are generally hydrophobic (they don’t mix with water), but they do not generally resemble the non-volatile oils we are used to interacting with, like cooking and fuel oils.

Because essential oils are prepared by distilling or extracting plant material, their actual content will depend on the plants they are produced from and the exact process used to extract them. Essential oils contain hundreds or thousands of different chemicals. While essential oils from the same type of plant made by different manufacturers will be similar, they can vary quite a bit, and no two extracts are likely to be exactly the same. There are also no government regulations controlling how these extracts are produced, or how pure the oils should be. It’s basically “let the buyer beware.”

Essential oils are used mainly for aromatherapy, and supporters of the practice believe it can treat many conditions, such as high blood pressure, hormone imbalances, stress, memory difficulties, and infectious disease. These oils are also sometimes applied to the skin (often during a massage) and some people even recommend drinking them or cooking with them to treat various ailments.

Do essential oils “work”?

Not really. There are some people (especially in Europe) who advocate aroma therapy as a beneficial form of “complimentary medicine”, which is a therapy that is added on top of standard evidenced-based medicine. However, the data doesn’t support it’s effectiveness for anything other than smelling nice. Nice smelling things are fun, so there’s that!

There are a few very specific uses for essential oils supported by science. Tea tree oil appears to be effective for the treatment of acne when applied to the skin, but it can also cause contact dermatitis, which kind of limits its value, since rashes aren’t much better than acne. Thyme oil has antibacterial properties when applied topically, but antibacterial soap is cheaper. Some essential oils are pretty good (but expensive) insecticides.

Are essential oils safe?

Now it gets complicated. Aroma therapy, which is the most common use of essential oils is safe as long as it is done in a well ventilated area. Problems start to arise when essential oils are applied topically (directly to the skin) or ingested.

Quite a few essential oils are irritants when applied to the skin. These can cause you to break out in rashes or even develop blisters if you put enough on. Irritant essential oils include cinnamon, clove, lemongrass, peppermint, citronella, tea tree, and mustard. It is also possible to develop allergic contact dermatitis to pretty much any essential oil. These allergic reactions can cause nasty rashes and are triggered by repeated exposure to the oils; common culprits for these types of reactions include, lemon, lime, angelica root, and balsam of Peru. Finally, several essential oils are known “photoirritants,” which are chemicals that are activated by sunlight into irritating or toxic substances, or “photosensitizers,” which are chemicals activated by sunlight into substances that can potentially cause allergic reactions. These oils include pretty much all citrus oils (orange, lime, lemon, etc).

Ingesting essential oils, either by eating food cooked with them or especially drinking them “straight” from the bottle carries the most risk. Many people think that because essential oils are “natural” they are harmless and/or good for you. This is not true. First of all, distilling or extracting the leaves of a plant in order to concentrate the chemicals inside of it is absolutely not natural. This concentrates some of the chemicals (the volitile oils) while eliminating many others, including the non-volitile, water soluble chemicals, and macromolecules and their building blocks (like proteins, amino acids, DNA, nucleic acids, sugars, and fiber). It takes about 3 pounds of lavendar flowers to produce a small bottle of lavender essential oil. It should come as no surprise that eating 3 pounds of lavender flowers might make you sick, and the same would be true for drinking a small amount of lavender essential oil.

Secondly, nature is actually really good at creating poisons. Many of the most poisonous substances known are natural, and chemical warfare is extremely common in the plant world. Two of humankind’s favorite chemicals – caffeine and nicotine are manufactured within plants as pesticides to keep insects away. Ricin (from the castor plant) and digoxin (from oleander) are two of the most toxic substances on earth. Just because it comes from a plant does not mean it’s safe.

Based on this, it should come as no surprise that many essential oils are not safe to ingest. Wintergreen, peppermint, tea tree, eucalyptus, nutmeg, and camphor oils can all cause serious toxicity when ingested. To make matters worse, since essential oils aren’t regulated, it’s impossible to tell how much of the dangerous ingredients is present in a particular product. There’s variability in the contents of oils from manufacturer to manufacturer and lot to lot, so just because you have ingested an oil without issues before, you can’t be certain that you’ll always avoid serious side effects the next time you ingest it. It’s like a botanical roulette.

The graphic below highlights some of the many potential side effects of common essential oil preparations. This is not an exhaustive list, so just because you don’t see a particular oil below does not mean it is safe to use.

What’s the bottom line?

While aromatherapy has not been shown to be an effective treatment for anything other than olfactory boredom, it is generally safe to inhale low levels of essential oils in a well-ventilated area. However, applying any essential oils directly to the skin should be avoided. Besides causing irritation, there is a risk of developing skin allergies over time. If you’re absolutely dead set on using these oils topically, avoid the irritants listed above and stop using them immediately if you develop a rash or blisters.

Cooking with essential oils that are common food ingredients is fine as long as you keep the levels low. Remember that these extracts contain highly concentrated chemicals – they are way more powerful than fresh ingredients – you only need a little to get the desired flavor. Essential oils can add to the flavor of your cooking, but there is no evidence they will provide a therapeutic benefit at all.

Ingesting essential oils directly is a bad idea. Many are toxic, and the lack of regulations and industry standards make it impossible to know how the concentration of potentially dangerous chemicals from an individual plant you may be consuming. Under no circumstances should you ingest undiluted essential oils, unless you think the emergency room in your town smells nice.