Essential oils have been used by people around the world for centuries for everything from religious purposes to healing the sick. Today, people rely on essential oils to improve health, including to improve relaxation and sleep, to improve digestion, and to improve the skin. Because of their high concentration, essential oils often are used with a diffuser that releases molecules of the essential oils into the air that you inhale and come into contact with. The oils enter your body and immediately begin to work to help improve your health.


With more than 50 hours spent researching and testing top products on the market, we concluded that the Smiley Daisy – Hibiscus is the best essential oil diffuser available. Three years after we first tested it, it’s still the best on the market. From the new crop of diffusers in 2019, we also like the InnoGear diffuser. This one in particular is great for larger spaces.

How we selected finalists to test

We spent more than 40 hours researching essential oil diffusers in order to find the best products to test. We started by looking at the biggest brands in the category (such as dōTERRA), then expanded our search through subreddits like r/aromatherapy and r/essentialoils.

We also read through several essential oil and aromatherapy internet forums, read studies and articles about the benefits of essential oils and diffusing those oils, and read about the diffusers that industry experts recommended.




Once we knew what to look for, we narrowed our search with a few more criteria. Each diffuser needed to meet the following requirements:

Have an automatic shutoff feature

Operate for at least 4 hours

Have a water capacity of 120ml or more

Come with a trustworthy manufacturer’s warranty

From there, we factored in positive reviews on Amazon and by professional reviewers as well as several interviews with brand representatives to determine which products we should test in-house.

In 2019, we looked for updated products that would fill a larger room and run for a longer time. We’re still happy with our 2016 top pick for most situations, but we found a new runner-up that will run even longer.

What exactly is an essential oil diffuser?

There are several different types of essential oil diffusers on the market. For this article, we focused on ultrasonic diffusers. Ultrasonic diffusers are best for diffusing essential oils because they do not utilize heat in the production of vapor. Since heat can have a negative effect on essential oils, ultrasonic diffusers are the best way to get the full benefit of diffusing essential oils.

Ultrasonic diffusers work by vibrating the water in such a way that it vaporizes into the air. Since the essential oils are mixed into the water, they are carried along with the water. Ultrasonic diffusers generate the vapor without any heat, which best preserves the integrity of the essential oil.

Diffusers are better than any scented candle, because you can put more than 100 different essential oils into them. You can even combine two or more essential oils to create a unique blend.

The difference between a diffuser and a humidifier

While a diffuser uses the same mechanism and adds a small amount of humidity into the air, the design of an ultrasonic humidifier is different.

An essential oil diffuser has a much smaller tank of water, usually somewhere between 80ml to 500ml. This means that the humidifying effects of a diffuser are relatively minimal when compared to a humidifier.

Unlike a humidifier, a diffuser is made from materials designed to hold essential oils. Crystal-clear acrylic water tanks let you see how clean the water is in your humidifier, but discoloration and cracking are common results of experimentation with essential oils. It’s possible to make a humidifier with a tank that can stand up to the organic compounds in common essential oils, but none of the models we tested in our humidifier review are designed to do so.

We did test some humidifiers that use a small heated pad to release the volatile compounds of an essential oil into the air without adding it to your water tank. Many essential oils change when heated, though. For those who want aromatherapy benefits and humidity, it is best to use an ultrasonic essential oil diffuser and a humidifier.

Benefits of essential oils

Essential oils have been used for thousands of years, from cultures as far-reaching as Ancient Egypt and India. These oils have been used for a variety of purposes, from spiritual to medicinal, and there are a significant number of modern scientific studies that support the theory that essential oils can be beneficial in a number of very real and quantifiable ways.

The following are just a few examples of the types of benefits that essential oils can provide:


Eucalyptus has been used across many cultures and is often used in over-the-counter medications. When placed near the sinuses or on the chest it helps with congestion and sore muscles. Eucalyptus is particularly useful for diffusers like the ones we are testing — especially when used for congestion.


Lavender is typically used for bruises, cuts, and skin irritation. Studies also show that the scent can reduce levels of the stress hormone cortisol. Application on the skin has its uses, however lavender is popular for diffusers because it can create a soothing, relaxing scent in a room.


Used in many OTC remedies, peppermint can be added to beverages and soothe the stomach. Studies show that peppermint increases oxygen levels in the blood, and can help a person be more aware.

Tea Tree

Tea tree oil is commonly used directly on the skin, and can be used for everything from acne to fungal infections.

Lots of others

There are literally hundreds of essential oils to choose from, some more useful than others. We recommend you do some research to find a few essential oils that will work best for you. When researching and testing the best essential oils, we discovered that quality can greatly vary by brands. Proper use and selection are required to maintain safety and to properly enjoy the benefits of these oils.

Do you need an essential oil diffuser?

A surprisingly small number of people actually know what an essential oil diffuser is. When we conducted a poll, only about half knew what an essential oil diffuser was.

That said, diffusers are gaining popularity due to a growing interest in the health benefits of essential oils, as well as the fact that scented candles are not as safe as many once thought.

The health benefits of essential oil diffusers

For many essential oils, there are different benefits attributed to applying them directly on the skin, versus diffusing them into the air. Some essential oils shouldn’t be placed directly on the skin at all.

Essential oils serve a number of purposes, including the following:


Essential oils are used for everything from relaxation (lavender) to pain relief (rosemary) to decongestants (peppermint and eucalyptus). By diffusing these oils into the air, you can gain the benefits for hours without needing to reapply the oils onto your skin.


There’s a reason why many spas have a distinctive smell — they’re using essential oils! Oils such as tea tree oil have been used for centuries to create the ambiance of a calm, safe place.

Insect repellant

Many people are already familiar with the fact that citronella is a useful mosquito repellant. However, there are lots of other essential oils that work as well — which is a good thing if you’re not a fan of the citronella scent!

Essential oils that act as insect repellants include:

Cedarwood and eucalyptus for fleas

Thyme, juniper, and rose geranium for ticks

Citronella and peppermint for mosquitos

Once again, it’s worth mentioning that while there are candles that can perform many of the same functions as the oils listed, essential oils (especially 100% pure oils) contain none of the harmful chemicals found in many scented candles currently on the market.

Essential oils vs. scented candles

Some people think that essential oils are out of their price range. After all, when people think “essential oils” they often image an expensive day spa. However, essential oils are in fact significantly less expensive than scented candles.

For the math enthusiasts, here’s a breakdown:

A 22-Ounce Yankee Candle costs about $27 on Amazon, and is guaranteed to burn for somewhere between 110 and 150 hours. If we take the high end (150), and divide by the cost ($27), we get a cost of 18 cents per hour.

The essential oil math is a little bit more complicated.

There are approximately 20 drops in a milliliter of Lavender essential oil, and 29.574 milliliters in an ounce. This comes out to about 591 drops per ounce.

A four ounce bottle of Lavender essential oil costs about $10.50 on Amazon, which means you can purchase 2,364 drops of Lavender essential oil for $10.50, at a cost of $0.0044 per drop.

Smiley Daisy recommends that we use about 3 drops of oil per 100ml, which means in the 350ml Hibiscus tank, we would need 10.5 drops, which we will round up to 11 drops. At $0.0044 per drop, those 11 drops cost $0.0484.

A 350ml tank lasts somewhere between 6 and 7 hours. If we estimate conservatively, that means the 11 drops will last 6 hours. Since the cost of the 11 drops is $0.0484, then the cost per hour is $0.0081 cents.

This means that the product cost for an essential oil diffuser is 4.5% of what it would be for a scented candle. When put into the context that essential oils have health benefits and scented candles have potential health risks, the choice is easy — even when we account for the electricity costs of a diffuser.

Research on the dangers of scented candles

There is a growing body of research which indicates that scented candles are not as safe as many think. It’s not just soot: many candles release harmful metals and compounds into the air — including lead, acetaldehyde, and formaldehyde.

While there are scented candles that do not release these harmful chemicals, a significant number do. This issue has underscored the value and importance of finding alternatives to candles.

If you currently use scented candles for anything from aromatherapy to ambiance, research your brand of candle to ensure it does not contain chemicals that could be harmful to you or your family.

A better option would be to switch over to an essential oil diffuser, which provides many of the same benefits as a scented candle. If you strongly prefer the ambiance of a flame to the swirling mist of a diffuser, think about putting an air purifier in the same room to give your lungs a break.

Important features to consider

There are a lot of essential oil diffusers available online. In fact, there are more than 32,000 essential oil diffusers available on Amazon alone. With so many products to choose from, narrowing the field to a few finalists can feel overwhelming. That’s why it’s important to filter for only the best quality and best value diffusers.

First, determine the size of the room you want your diffuser to cover. Most (high-quality) diffusers list the size of a room in which they can effectively diffuse.

“Too much” diffusing is not a common problem with essential oil diffusers, especially since many offer a way to reduce output if necessary.

It’s also important to look at the water capacity of a diffuser, along with the estimated operating time. The operating time informs you of how long you can expect the essential oil scent to last in the room, while you can estimate the amount of water (and oil) diffused by taking the water capacity and dividing it by the operating time (e.g. 100ml and 2 hours would mean 50ml diffused per hour).

It’s also important to take into consideration the build quality of the diffuser you buy. Essential oils can be corrosive to some plastics, which means that a cheaply-made diffuser might break down after only a few months of use. All high-quality diffusers use polypropylene, or another strengthened polymer or material, to ensure the longevity of the product.

Ease of use is another important consideration. This includes both setup (which should involve little more than putting water and your preferred essential oil into the diffuser) and clean up.

The size, or dimensions of a diffuser might not matter to everyone. However, for those with limited space, it might be worth looking into a diffuser with a smaller footprint. Similarly, a noisy diffuser can be distracting in an otherwise-quiet setting — such as a yoga studio or even your bedroom.

Features such as a timer and ambient lighting can be a nice touch, and are worth taking into consideration when comparing one diffuser to another.

How we tested

In order to determine the best aromatherapy diffuser on the market, we ordered our seven finalists and put them through a series of tests in our San Diego office.

The first thing we did was open the box and read the instruction manual.

Next, we looked at the pieces and assessed how easy it would be to set up the diffuser. We also took into consideration the build quality of the diffuser.

After that, we looked at the settings and options available on the diffuser, including auto-off, lighting, timers, etc. We also took note of how intuitive the controls were, and whether we needed to actually refer to the instruction manual more than once.

We also checked to confirm that the specs and features listed on each diffuser’s product page matched the product itself. Specifically, we checked ambient lighting, operating time, water capacity, timers, and automatic shutoff when the water reservoir is depleted. Fortunately, all seven finalists held up to expectations, so we moved on to differentiating between their diffusing performance.

To test each of the diffusers, we closed the doors and windows in our conference room, which measures 21 by 10 by 12 feet, for a total of 2520 cubic feet and 210 square feet.

We then filled the first diffuser with water and the recommended number of drops of essential oil (we used sweet orange oil for our testing because it has a distinct and easily-detectable scent), making sure to use the same ratio of water to oil for each diffuser.

With the conference room closed off, we put the first diffuser at one end of our 8-foot conference table and calculated how long it took for the scent of the sweet orange oil to reach the other side of the table — with three judges to ensure as accurate a measurement as possible.

The notable performers in this test were the dōTERRA and PureSpa – Deluxe, both moving the scent quickly through the room. This doesn’t seem correlated to having a more diffuse plume of vapor or a faster (and thus louder) fan.

On the other end of the scale, PureSpa’s Compact model put out so little vapor that it took eight minutes to reach the other side of the room.

After measuring how long it took for the scent to reach the other side of the conference table, we left the room and let the diffuser run for 30 minutes with the doors and windows closed. We went into the room and touched the diffuser to determine if any parts were warm, and also used a decibel meter to measure the noise level from an inch away.

Note that the main sound coming from a diffuser is, in most cases, bubbling water. The models with the loudest noise level, like the Greenair and InnoGear, also have a small fan to help the vapor spread through your room.

Best overall: Smiley Daisy – Hibiscus

While all seven of the diffusers we tested do a good job of releasing essential oils into the air, the Smiley Daisy – Hibiscus was easily the best of the pack. The diffuser’s short stature, coupled with strong build quality and four sturdy rubber feet means that this diffuser won’t get knocked over very easily.

What makes the Hibiscus really stand out is the vapor output it produces, as well as the quality of that output. The water capacity of the Hibiscus diffuser is 350ml, which is more than double the capacity of most other diffusers we tested. With a maximum run time of between 6 and 7 hours, this translates to approximately 55ml of vapor per hour.

The diffuser also produced a strong stream of vapor, which could be seen as much as 20 inches from the table, or about 16 inches above the spout on the diffuser. It’s

The large capacity and strong vapor stream of the Hibiscus made a noticeable difference during our testing. We found that there was a strong scent — about as strong as when the diffuser was on — for about 15 minutes after we turned the diffuser off. The scent remained quite noticeable until the 30 minute mark, and a lingering scent remained until almost an hour after turning the diffuser off.

Operation of the Hibiscus is simple as well. The instruction manual has very straightforward instructions, and using the product feels intuitive right away. There are two separate buttons on the front of the diffuser — one for turning the diffuser on or off (including a setting for a 2 hour timer), and a separate button for turning on and off the light.

The light itself offers seven different color options, which can either cycle or be locked onto one color. The light itself isn’t particularly bright, so it could serve as an effective night light without disrupting sleep. (Especially if you choose the red light, as we found out in our night-light research.)

Finally, the Hibiscus essential oil diffuser is quiet. In our office, which measures about 40 decibels with the doors and windows closed, the diffuser only generated 46.5 decibels of noise.

Smiley Daisy also offers a 180 day warranty, which ensures that, if you’re one of the unlucky few that get a defective product, you’ll be able to get a replacement at no cost and with no hassle.

Overall, the Smiley Daisy Hibiscus Essential Oil Diffuser offers impressive build quality and the best overall performance of the essential oil diffusers we tested. At a price point below $40, the diffuser is a great value as well.

What we didn’t like about the Hibiscus

While the Hibiscus was our best pick, there were a couple of negatives about the product. The biggest potential problem is the large footprint of the diffuser. Unlike most diffusers, which utilize vertical space in their design (and particularly for their water reservoirs), the Hibiscus is short and wide, measuring 8.3 by 6.6 inches (and only 3.2 inches of vertical height).

In addition, the light generated is minimal, functioning more as a design element than an actual source of light.

All that said, these negatives are very minor when compared to the overall package. We’ve been using the Hibiscus for three years now, and it’s still humming along cheerfully.

Key takeaways:

The Smiley Daisy – Hibiscus has a strong build quality with sturdy rubber feet.

It has double the water capacity of most other diffusers, which means less refilling.

Smiley Daisy achieved the strongest vapor release rate in our tests.

With cycling seven colored light options, this is a worthy mood-light.

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