Essential Oil Diffusers: An Overview

Do they work? Are they worth it? We look at what the research says.

Long Article

The Big Takeaway

Essential oil diffusers might help you fall asleep, especially if you already have good sleep habits. If you use one, use lavender, and try it around your pillow if you don't have a diffuser. Don't use diffusers in a room with pets.

This is a very short summary of a very complex and controversial research area. If you’d like to know the details and see the studies, please stay and dive in!

What is an Essential Oil?

An “essential oil” is a hydrophobic (water repelling) plant oil that turns into vapor when it’s heated.  Unlike fatty oils like olive oil or vegetable fats, essential oils evaporate completely without leaving a stain on filter paper. These highly-concentrated compounds are named for the “essence” of the plant’s smell that stays with the oil, and different plants produce very different chemicals in the extraction process.

Some essential oils are “active substances,” meaning they have a chemical or biological effect. One widely-used compound is thymol, the essential oil from thyme, which is used as a preservative, antimicrobial additive, and historically as a deworming treatment. Many essential oils are “inactive substances,” meaning they don’t have a biological effect or therapeutic value, though they may still smell nice.

You may see essential oils marketed as “non-chemical alternatives” to “drugs;” if you do, beware! Anything you take that helps or hurts your body is an active ingredient, and it doesn’t matter if it’s being sold as a pharmaceutical, supplement, homeopathic treatment, essential oil, or remedy; they’re all chemicals. They’re just regulated differently.

Making Essential Oils

There are a few ways to extract essential oils from plants – the most common is distillation. In distillation, steam is passed through the plant parts, vaporizing the oils and sending them through a tube into a condensing chamber.  Because the oils are water-repelling, they condense as a floating layer on top of the water from the steam. The water under the oils is sometimes sold separately as a “herbal distillate,” such as rose water or witch hazel (see diagram).

Making Essential Oils
Essential Oil Distillation, adapted from Hafizmuar at English Wikipedia

Essential oils can also be extracted through “pressing” (squishing the plant until the oil comes out), and “solvent extraction,” which uses a chemical to draw out the oils. Solvent extraction is used when there isn’t enough oil for pressing and the compound is too delicate for distillation.

Are Essential Oils Safe?

It depends on what they are and how they’re used. Remember that essential oils are concentrated plant chemicals, and different plants make very different products. They may also contain active substances that can react with medication or cause allergic reactions. Here are some basic safety tips when using essential oils (note: this is not medical advice. If you are concerned about a health condition, or the interaction of an essential oil with your medication talk to your doctor before diffusing, consuming, or touching anything):

Essential Oil Safety in Diffusers

In general, commercially sold essential oils used in small quantities in the air (such as in a diffuser) are fine for adults as long as they’re not allergic to anything in the oil. Make sure to buy your oil from a reliable source and check that it is recommended for diffuser use.

On the other hand, essential oil diffusers can be very dangerous to pets. Many of our animal friends have a higher sensitivity to the chemicals in essential oils and the microdroplets produced by essential oil diffusers. There is very little reliable research on safe essential oils to use around pets, but a brief recap of oils known to be unsafe is provided below.

Essential oils that are known to be dangerous to cats

  • Cinnamon oil
  • Citrus oil
  • Clove oil
  • Eucalyptus oil
  • Sweet birch
  • Pennyroyal oil
  • Peppermint oil
  • Pine oils
  • Tea tree oil
  • Wintergreen
  • Ylang ylang

Essential oils that are known to be dangerous to dogs:

  • Pennyroyal oil
  • Pine oils
  • Tea tree oil
  • Wintergreen

Essential oils that are known to be dangerous to birds and reptiles:

  • Don’t use a diffuser in a room with birds and reptiles. They have sensitive lungs that are easy to damage and it’s not worth the risk, especially with the lack of safety research and high potential for harm. This also goes for scented candles, incense, etc.

In summary, diffusers can be great for people and not so great for animals, with a huge gap in research on pet safety. Use your diffuser in a room away from pets.

Essential Oils and Pets

Eating and Drinking Essential Oils – Don’t Do This.

A few essential oils are used as a flavoring additive in foods, with peppermint, lemon, and orange being the most common. That said, most essential oils are not food safe and can cause very serious side effects if ingested. Some of the more dangerous oils to eat are also the easiest to find, with camphor, clove, lavender, eucalyptus, thyme, tea tree, and wintergreen oils being particularly toxic if swallowed. Because of the deceptively sweet smell, children are among the most common victims of accidental essential oil poisoning, which can cause agitation, seizures, breathing problems, liver failure and brain swelling.

Do not eat or drink pure essential oils and keep them out of reach of children. They can be very dangerous, there are no benefits, and it’s not a good idea. Only use essential oils in food that are designed and marketed as food-safe and use them only in the quantities as directed.

Essential Oils on the Skin

Pure essential oils can cause “contact dermatitis” (pain, swelling, itching, and redness) if they’re rubbed directly on your skin. To use essential oils safely, add them in small amounts to a “carrier” that you know your skin will tolerate. Good carriers include fatty oils (olive, coconut, jojoba, sesame oils), fatty oil blends, and premade skin products like lotions. Avoid essential oils in all quantities if you know you have an allergy to the plant it is derived from.

Lotions, soaps, shampoos, and other cosmetic products that contain essential oils have already diluted them to safe levels, as long as you don’t have an allergy or sensitivity to the oil. Be aware that in all cases, children, pregnant women, and elderly persons can have a higher sensitivity and should use more care with any products containing active ingredients or allergens. Avoid or use veterinary guidance with any product containing essential oils for your pet.

What Does The Research Look Like On Essential Oils and Sleep?

Why Aren’t There More Studies on Essential Oils and Sleep?

The short answer here is expense. Well done studies that give a reliable answer on whether or not a product or drug works are very expensive, take a long time, and require a lot of investment. This investment can be worth it in a few situations, most of which don’t apply to essential oils:

  • Companies paying for a study: Companies will pay for a study if they can make a lot of money off the product – this is for products that are new, expensive, or have a patent limiting who can sell them. Essential oils are fairly cheap, easy to get, and have no limitation on where they can be sold. There’s also no reason to pay to study a product that people will already buy without the study.
  • Hospitals paying for a study: Hospitals may pay for a study if it is likely to significantly reduce their costs or improve patient outcomes. This may be true for essential oils, and some hospitals are doing this work – some results are promising, but none of the studies have shown enough of a cost-savings so far for very large studies to be funded. This doesn’t mean that they have no effect, but the effect may not justify the cost of a full study.
  • Research Institutions paying for a study (grant funding, university funding, etc): Essential oils are unlikely to have a big payoff for large university studies – they’re hard to control for (subjects know if they smell an oil or not), not new, and the effects may be subtle. Despite this, some institutions are studying essential oils for anxiety, and there have been some promising results. Most of the studies are small, and few of them are well done, but we’ll be taking a look at the better-quality research and the meta-reviews that summarize the essential oil results.

So in summary, research is being done by some hospitals and institutions, but the studies are usually small, and more information is needed. The studies have generally looked at the “true/false” part of the question – they’ve tried to see if essential oils work or don’t work, but not which ones work best, how much should be used, when they should be used, and what the best delivery is.

It’s also important to keep in mind that sleep and anxiety reduction are some of the few areas aromatherapy research has shown promise – aromatherapy has not been shown to cure any disease or illness. If you see claims that aromatherapy represents a miracle cure, or that it should be used instead of your doctor-prescribed treatment, run the other direction. Because it is unregulated, aromatherapy is an area with a lot of misinformation, incomplete information, and plain guesswork.

Sleep Studies – Lavender Essential Oil and Sleep

Lavender’s traditional association with sleep and relaxation has made it a common target for essential oil sleep studies (whether it really is the best smell to help you fall asleep needs a lot more investigation). Many of the studies on lavender have shown a lot of promise, but with this promise has been a lack of scale, design restriction, and replication.

Part of the issue with research on lavender is that many of the studies don’t have a “control group” (a group not using lavender at all), and the studies are not blinded (the participants and researchers know if they’re receiving the intervention or not). This means that people could be sleeping better because they feel that someone is helping, or because they feel less stressed because a doctor is caring for them, even if the lavender itself does nothing. This doesn’t mean that it doesn’t work, but it also doesn’t support it as a treatment.

As an example of this conflict, a small, 42 participant study on women in Korean nursing programs showed a significant improvement in falling asleep, reducing insomnia, and waking rested with lavender. However, rather than compare their sleep to students not using lavender, the study used a baseline week of no lavender, a week with a low concentration, and a week with a high concentration as their comparisons. This means the improved sleep by the third week could be caused by lower anxiety on working with the researchers, the placebo effect, or a range of other things in their environment. They’re was also no blinding – the participants knew when they received the treatment and exactly what treatment to look for to feel better.  None of this means that the lavender didn’t help – it means it might have, but more research is necessary, and this study has been cited in other papers looking at this effect.

More promising is a 2012 review study (study collecting other studies) that found a small-to-moderate benefit to lavender across a section of collected research. It found that more research needs to be done, and the effects are subtle, but suggested that lavender may help with faster, deeper sleep. It also found that a lot of the use of lavender is “self-administered,” meaning it’s something people do because they’ve heard about it and try it on their own, rather than going through their doctor. This isn’t necessarily a bad thing, but it makes it hard to figure out if lavender use can be tied to side effects. A 2014 review of general aromatherapy and sleep found that lavender, peppermint, and jasmine oils seemed promising, and also noted the need for more follow-up.

Lavender may also help with young children; a 2007 study found that lavender-scented bath oil was associated with infants crying less, relaxing, and looking at their caregivers more. This small study (30 participants, divided into three groups) also found that the effect might be more on the mother than the baby – mothers using lavender-scented oil spent more time touching their children than mothers who didn’t have the aroma present. A 2018 review of non-traditional approaches in sleep also referenced positive results for infants, while results in older children and children experiencing sleep problems were mixed and less supported.

Overall, lavender may help with falling asleep faster, especially if your sleep routine is already healthy. It’s not a cure-all, and probably won’t make a big difference in chronic insomnia or sleep disruption, but it might provide an extra boost to an otherwise good sleep environment.

As a side note, a 2011 study that came up from a typo found that lavender makes nervous sheep more nervous and calm sheep more calm. Whether genetic differences in humans impact their reaction to lavender in the same way has not been studied.

What is an Essential Oil Diffuser?

An essential oil diffuser sends small particles of water and essential oil (or just the oil) into the air, creating a mild smell in the room. There are three main types of diffuser:

  • Nebulizing Diffuser – these use a pressurized air current to create a vacuumed that disperses small particles of essential oil into the air. Unlike many diffusers, there’s no heat and no water, so the oil is a little bit less diluted.
  • Ultrasonic diffusers – this type uses ultrasonic vibrations to break the oil and water mixture into a fine mist of particles that disperses into the room.
  • Evaporative diffusers – these use heat or air currents to spread the essential oil. Unlike the other types, they’re not mechanical, and use simple methods (like sticks that soak up the oil, or candles containing the oil) to get the scent out.

Any of these will make your room smell like the essential oil of your choice. If you’re concerned about cost, evaporative diffusers are much cheaper and more readily available; if you want something more powerful, an electronic diffuser will give you more control and intensity.

Does Using an Essential Oil Diffuser Help You Fall Asleep?

Maybe! See above. There’s some research that shows some essential oils may help you fall asleep, especially if you have good sleep habits and are not suffering from chronic insomnia. Unfortunately, there’s a big lack of large, controlled studies on essential oil diffusers and home use, so a lot of this is guesswork. Most of the studies have used lavender, and it may help with anxiety, so if you’re going to try a diffuser, lavender is probably a good first choice for an essential oil scent.  

What Are the Alternatives to Using an Essential Oil Diffuser?

If you have pets in your room, or respiratory problems that make using a diffuser a less than perfect choice, you can still try aromatherapy as a sleep aid. One easy alternative is sleep masks that incorporate lavender, or jewelry designed to hold an essential oil fragrance. There are also lavender lotions, and the essential oil itself is pretty inexpensive if you want to mix your own (remember to use a carrier oil so that you don’t burn your skin). If you’re really having trouble sleeping, consider changing your sleep habits, cooling down your bedroom, or talking to your doctor. Your sleep is important and deserves a solid research foundation.

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