Essential Oils in a Diffuser: How to Use Them and What They Do

What Are Essential Oils?

Essential oils are concentrated extracts from a range of fragrant plants like lavender, peppermint, and eucalyptus. The oils are extracted from the plants through methods like mechanical pressing or distillation, the latter of which uses heating or cooling to take the oil out of the plant (Farrar, 2020).

Essential oils have been used for centuries in aromatherapy. Aromatherapy is a complementary health approach based in part on the idea that smelling certain fragrances can cause the release of neurotransmitters, chemical messengers that can trigger a sense of well-being (Fung, 2021).

Terpenes, which are plant-based compounds responsible for the way plants smell, are a primary basis of essential oils and are believed to play a part in the therapeutic effects of aromatherapy (Ali, 2015).

Different terpenes are associated with different scents and mind-body effects. For example, research suggests that the terpene limonene—found in lemon essential oil—may relieve labor pains, aid in controlling nausea and vomiting, and have stimulating properties that help with elevating low mood. Meanwhile, the terpene linalool—found in flowery essential oil scents like lavender and clary sage—has been shown to produce calming effects (Ali, 2015).

How to Use Essential Oils

To diffuse, by definition, is to spread something across a large area. Essential oil diffusers do just that, taking a few drops of concentrated essential oil and disseminating them into the air over an extended period of time. There are a few different types of essential oil diffusers—from electricity-free reed diffusers that soak up essential oils and disperse them around the room, to heated diffusers (also called essential oil warmers) that warm up the oil until it evaporates into the air.

Perhaps the most popular type of diffuser is the ultrasonic diffuser, an electronic device small enough to sit on your desktop or bedside table that uses water to diffuse essential oils into the air. While the instructions for how to properly use an ultrasonic diffuser may vary by brand (and you should always read the manufacturer's instructions), they're typically pretty simple to set up, according to Erik Nelson, ND, a practicing naturopathic doctor and integrative medical advisor at Fullscript, an online treatment plan tool for integrative health providers.

Before setting up your diffuser, it can't be emphasized enough that you need to make sure it's unplugged before filling it with water. "It depends on what type of diffuser you use, but they typically have a water basin with a fill line on the interior," Nelson told Health. "You don't want to go past the fill line."

When filling your diffuser, it's important to opt for filtered or bottled water, as "hard water" (water with a high mineral content) from the tap may damage the diffuser over time, per Nelson.

The next step is to add a few drops of your chosen essential oil(s) to the water basin. Again, Nelson advises anyone using a diffuser to check the instructions to determine the proper "dose" of essential oils to add. When it comes to essential oils, you don't need to use too much at one time.

"The first thing you need to remember about essential oils is that they're super concentrated, so you only need a couple of drops. Any more than that is probably overkill," said Nelson.

Where you place your diffuser will depend on your reasons for using it. If you're wanting to enjoy aromatherapy as part of a bedtime wind-down routine, you should place the diffuser in your bedroom and use it at the end of the day. If you're using a diffuser in hopes of feeling more focused during the workday, you should opt for placing the diffuser in your office (just be sure to keep it away from other electronic devices to reduce the risk of them getting misted).

After picking a location for your diffuser, you can close the lid and turn it on. Essential oil diffusers are pretty low maintenance—so once it's on, all that's left to do is go about your day (or night) and let the device do its thing.

As for if and how you should clean your diffuser between uses, Nelson said to check the manufacturer's instruction manual that comes with your device. Certain solvents or cleaners may or may not be recommended depending on your device.

How to Pick an Essential Oil for Diffusing

Picking high-quality essential oils is key to a safe and relaxing aromatherapy experience. And while it may seem obvious, you should only use scents of which you personally enjoy the smell.

The essential oil market is not regulated by the US Food and Drug Administration, which means that purity and quality aren't guaranteed. When shopping for essential oils, your best bet is to do some research and look for oils that were produced using "clean" distillation methods, Nelson said. These methods avoid the use of harsh solvents like acetone, which can be harmful to breathe in (Umeh, 2021).

"Clean" distillation methods to look for include:

Cold-pressed distillation
Steam-distilled extraction
Supercritical or subcritical CO2 distillation
Subcritical CO2 distillation

When looking for an essential oil to use in your diffuser, it's crucial to pick a formula labeled as being for aromatherapy use only. "The bottle will usually say 'for external use' or 'for aromatherapy purposes,' and you should never use outside of that recommendation," said Nelson.

If you're new to aromatherapy or using essential oils for the first time, it may take some trial and error to lock down your favorite scents or scent combinations. Understanding the basic science behind aromatherapy can help guide you to finding the optimal fragrance based on the effects for which you're looking.

The terpenes that give plants their scent are the biggest make-up in essential oils (Koyama, 2020). All scents found in nature are composed of varying combinations and concentrations of different terpenes.

Examples of terpenes and the essential oils they are found in include: (Ali, 2015)

Linalool: found in high concentrations in lavender and ylang ylang essential oils
Limonene: found in high concentrations in lemon and orange essential oils
Menthol: found in high concentrations in peppermint/spearmint essential oils
Pinene: found in high concentrations in rosemary essential oils

A limited body of research in humans and animals suggests that terpenes interact with the brain in particular ways and may affect the levels of neurotransmitters like serotonin and dopamine, which are associated with mood and stress (Cox-Georgian, 2019).

When picking an essential oil, it helps to know what terpenes exist in specific scents so that you can understand the scent's potential therapeutic benefits. For example, linalool-rich essential oils like ylang ylang and lavender are commonly used in aromatherapy to induce relaxation and help achieve a sense of calmness. Meanwhile, citrus essential oils with high concentrations of limonene have been shown to have mood-boosting effects (Fung, 2021).

Benefits of Using Essential Oil Diffusers

You may have heard advocates of aromatherapy promise that essential oils can treat symptoms of anxiety and depression. Skeptics, on the other hand, may write off the oils entirely as a marketing sham.

The truth about essential oils is likely more nuanced than that. Aromatherapy has been used for centuries, and there is a growing body of modern research suggesting that inhaling essential oils may have real therapeutic benefits. Still, other studies show no improvement in symptoms (Freeman, 2019).

Currently, high-quality clinical studies on the topic are limited. The evidence that does exist is, for the most part, found in animal studies, has only a small sample size, is based on mostly subjective outcomes, and used inadequate study methods (Freeman, 2019).

With that said, there are a few studies that suggest there can be therapeutic benefits to inhaling essential oils.

One small, placebo-controlled study found that pregnant women who inhaled lemon essential oil as soon as they felt nausea had a reduction in the intensity of vomiting and retching (Yavari, 2014). Another small study found that participants who inhaled bergamot essential oil diffused with water had lower salivary levels of cortisol—widely known as the stress hormone—and reported improvements in fatigue and negative emotions (Watanabe, 2015).

Research and anecdotal evidence in humans and animals suggest that inhaling lavender essential oil may help induce relaxation, decrease heart rate, relieve anxiety, and improve mood. A range of small, randomized aromatherapy trials have shown that inhaling lavender helped to reduce anxiety among patients with anxiety relating to chest tube removals, cosmetic procedures, intensive care unit stays, and upcoming surgeries. However, it's important to note that none of these subjects had an actual anxiety diagnosis (Malcolm, 2017).

Aromatherapy with lavender essential oil may also be particularly useful when used as a complementary treatment. One study concluded that lavender aromatherapy could be used as part of a multidisciplinary treatment plan for pain after a Cesarean section. The researchers noted that patients who inhaled lavender essential oil had a decreased heart rate and increased level of satisfaction with pain compared with patients in the placebo group (Olapour, 2013).

Risks of Using Essential Oil Diffusers

Essential oils are natural, plant-based products, so you may be inclined to believe that they're risk-free to use. Unfortunately, that's not the case.

If you have any pets at home, Nelson stressed that you need to check with a vet before using an essential oil diffuser around your pets. Certain oils may be toxic to animals when inhaled.

People who are pregnant, breastfeeding, or have young children should also err on the side of safety and check in with a healthcare provider before experimenting with essential oil diffusers.

Anyone with allergies should also do their research. For example, someone with a pine allergy should likely avoid products that contain pinene, according to Nelson.

In general, it's important to not use essential oils topically without diluting them in a carrier oil, like coconut, rosehip, or jojoba oil. Some essential oils, like tea tree oil, can cause serious skin irritation if applied directly from the bottle to the skin, per Nelson.

"If you notice any changes or negative health effects from using an essential oil diffuser, you should stop using it," said Nelson. "Make sure you open your windows to get good ventilation in, and contact a medical professional."

Summary

Essential oil diffusers are an accessible and relatively low-risk way to enter into the ancient world of aromatherapy. While high-quality research on essential oil diffusers is limited, there is anecdotal and clinical evidence suggesting that inhaling essential oils may have some therapeutic benefits. Being an informed consumer is particularly important when shopping for essential oil products and ensuring a safe experience. Keeping these things in mind will help set you up for a relaxing and realistic experience—aromatherapy, as intended.

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