How to Use an Essential Oil Diffuser: What the Research Shows

To use an essential oil diffuser, fill the tank with water to the maker's line, add oil as the manual says, and run it for short sessions in a ventilated room. This guide covers how, and what Health Canada, a children's hospital and the American Lung Association say about doing it safely.

We sell an Aroma Diffuser Marmo, so read this with that in mind. Where the evidence is thin, or where our own listing says little, this guide says so. For the wider scent question, see our guide to how scents affect mood, sleep and stress.

How Do You Use an Essential Oil Diffuser?

Fill it with water, add oil as the manual says, and run it in short sessions. The steps below follow the sources in this guide, not a lab test of our own.

1. Check who is in the room. The Children’s Hospital of Philadelphia advises limiting aromatherapy to children over 3, saying there is not enough clinical research on younger ones. It lists young children, sensitive adults and pets as people the airborne oils can irritate.
2. Check the oil. Health Canada lists 14 oils and extracts it proposes may be harmful in DIY aromatic diffusers. Look yours up before you fill the tank.
3. Fill with water and add the oil. Follow the maker's fill line and drop guidance. We found no authoritative source giving one number of drops that suits every diffuser, so we do not give one.
4. Run it for a short time. Start with about 20 minutes and open a window or door. Stop if anyone coughs, or has throat, eye or nose irritation.
5. Empty the tank afterwards. CHOP warns that standing water can breed bacteria. Pour out leftover water and let the tank dry.
6. Store the bottle safely. Health Canada says to keep essential oils out of reach and sight of young children and pets.

Does Diffusing Essential Oils Actually Work?

The evidence is thin. A US government fact sheet says it is not known whether aromatherapy helps with insomnia because little rigorous research has been done.

• The mood study: The National Center for Complementary and Integrative Health describes one study of lemon and lavender scents in people under stress. Lemon had a positive effect on mood, but neither scent affected stress indicators, immune markers or pain control.
• Claims about disinfecting: The American Lung Association says research suggests the germ-killing effect of some oils, tea tree in particular, only appears in the first 30 to 60 minutes after evaporation starts, so diffusing to disinfect is ineffective.
• The gap: The same article says most aromatherapy research looks at a single oil, while people often combine several, and that research on combinations is limited.

Is It Safe to Diffuse Essential Oils?

It depends on the oil, the room and who is breathing it. Health Canada says natural does not always mean safe, and the American Lung Association says concentrated oils can irritate the airways.

• Airway irritation: The Lung Association says inhaling concentrated oils can cause coughing, nose and throat irritation or shortness of breath, and people with asthma or COPD may be more susceptible.
• Heart and lung data: It cites a 2022 study of 200 people in which those who inhaled essential oils an hour or more a day had higher heart rate and blood pressure and lower lung function. That is an association, not proof of cause.
• Combined oils: It also notes that when some volatile compounds combine, secondary pollutants such as formaldehyde, a known nose, throat and lung irritant, may form.
• Regulation: It says essential oils are not regulated in the United States, so the contents and concentration of a bottle are not guaranteed.
• Water-based diffusers: CHOP advises avoiding water-based diffusers around young children, sensitive adults and pets, because the aerosols can irritate the lungs, eyes and skin. Ultrasonic cold-mist models, ours included, use water, so this advice applies to them.
• Fire: CHOP says never to use heat to diffuse oils because essential oils are flammable.

Which Essential Oils Does Health Canada Flag for Diffusers?

Fourteen oils and extracts. Health Canada's draft risk assessment proposes they may be harmful when used in DIY aromatic diffusers, among other uses.

• The list: Bay oil, cade oil, cedarwood oil, cork tree extract, jasmine oil, jonquil oil, mimosa oil, myrrh oil, sage oil, tarragon oil, Verbena officinalis extract or oil, violet oil, wintergreen oil and wormwood oil.
• The status: Health Canada says the assessments are not yet final, and the page was last modified on February 28, 2025. Check it for updates.
• The label problem: Some oils may not appear on product labels when used as fragrance ingredients, where they can be listed only as fragrance or parfum. If unsure, Health Canada suggests contacting the maker.

How Long Should You Run a Diffuser?

Short sessions are the safer default. We found no official time limit, but the sources point toward less rather than more.

• Scent fatigue: CHOP says the brain ignores a smell after 20 minutes, which can lead people to add more oil because they no longer smell it. It links this to rebound headaches and other symptoms.
• Heavy daily use: The 2022 study cited by the Lung Association found worse readings in people who inhaled oils an hour or more a day.
• If you have asthma or COPD: The Lung Association says adding anything to the air you breathe, essential oils included, is not recommended, and that you should consult your healthcare professional first.

What Does Our Own Diffuser Page Say?

Not much. Our Aroma Diffuser Marmo page calls it a marble-patterned variant of our ultrasonic line with a cold-mist mechanism and a reservoir equal to about 100 ml. That is all it says.

It gives no run time, no auto shut-off detail and no cleaning instructions, so follow the maker's manual that comes with it. We are reviewing the listing. Until then, treat this guide, not the product page, as the safety reference.

When Should You Talk to a Doctor About Essential Oils?

Talk to a doctor before diffusing if you have asthma or COPD, and get help right away if anyone swallows an essential oil. This guide is information, not medical advice.

If someone swallows an essential oil or a product containing it, call your local poison control centre or emergency services at once. Stop diffusing and move to fresh air if anyone develops coughing, breathing trouble or irritation.

Frequently Asked Questions

How do you use an essential oil diffuser?

Fill the tank with water to the maker's line, add oil as the manual directs, and run it in short sessions in a ventilated room. Empty the tank after use.

How long should you run a diffuser?

We found no official limit. CHOP notes the brain ignores a smell after 20 minutes, and a 2022 study linked an hour or more of daily inhaling to worse heart and lung readings.

Are essential oil diffusers safe for pets and children?

Use caution. CHOP says airborne oils can irritate the lungs, eyes and skin of young children, sensitive adults and pets, and advises limiting aromatherapy to children over 3.

Which essential oils should you avoid in a diffuser?

Health Canada's draft assessment proposes 14 oils and extracts, including cedarwood, sage, myrrh and wintergreen, may be harmful in DIY aromatic diffusers. The assessment is not final.

Do diffusers help you sleep?

The evidence is thin. The US National Center for Complementary and Integrative Health says it is unknown whether aromatherapy helps insomnia because little rigorous research exists.

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