Diffusers, Indoor Air Quality and Exposure at Work
What chamber studies, the EPA and an aromatherapy association say about essential oil diffusers and indoor air, and what is documented about skin reactions in people who work with the oils.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Urgent first
Call 911 for trouble breathing, a swollen throat or tongue, a seizure or collapse. If an oil was swallowed, call Poison Help at 1-800-222-1222. People with asthma should also read diffusers and breathing problems.The short answer
A diffuser adds scent compounds and, for some types, tiny particles to indoor air. A Canadian chamber study measured this for an ultrasonic diffuser. [1] We did not find a study that links everyday home diffuser use to a measured health outcome in people. Proper evidence not found for workplace exposure limits for essential oil vapors: we looked at the EPA, NHS, FDA and NAHA pages and found none. This page reports what was measured and what experts say, and it gives no "safe amount of diffusing".What was measured
| Question | What the source found | Type of evidence |
|---|---|---|
| What comes out of an ultrasonic diffuser? | In a chamber study using lemon, lavender, eucalyptus and grapeseed oils, the most abundant compounds were d-limonene, eucalyptol and linalyl acetate, in milligram amounts over 15 minutes. [1] | Laboratory chamber study |
| Does it add particles to air? | Each oil had its own particle profile. [1] The authors' modeling suggests reasonable use can contribute substantially to fine particles indoors, depending on the oil and the water type. [1] | Laboratory plus modeling |
| Does water matter? | Fine-particle emission rose about fivefold with eucalyptus oil when tap water was used instead of deionized water. [1] | Single experiment |
| Does it harm health? | Not measured in that study. | Insufficient evidence |
A chamber test of one diffuser model is not a measurement of any particular home.
Indoor air in general
The US EPA says concentrations of many volatile organic compounds (VOCs) are consistently higher indoors, up to ten times higher, than outdoors. [2] It lists symptoms associated with VOC exposure, including nose and throat discomfort, and lists moth repellents and air fresheners among the sources. [2] It advises increasing ventilation when using products that emit VOCs. [2] It also states that no federally enforceable standards have been set for VOCs in non-industrial settings. [2]Essential oils release volatile compounds, as the chamber study measured. [1] The EPA page is about VOCs as a group, not about essential oils, and does not say that oils are harmful or harmless.
Exposure at work
Skin, not air, is where we found documented workplace harm. A report from Australia and New Zealand describes allergic contact dermatitis to essential oils in three aromatherapists and one chemist, mostly affecting the hands, with sensitization to multiple oils. [6] The authors say workers in this industry should be aware of the sensitization potential of these products. [6] Four people is a case series, not a measure of how common this is. See skin reactions, allergy and sensitization and oils in workplaces, spas and schools.Frequently asked questions
Do diffusers pollute indoor air?
A chamber study found one ultrasonic diffuser released compounds and fine particles, with amounts varying by oil and water. [1] The effect on health was not measured.
Is it safe to run a diffuser all day?
We found no source that gives a safe duration. NAHA mentions prolonged exposure to high vapor levels as a possible cause of headaches and nausea. [3]
Should I ventilate the room?
The EPA advises increasing ventilation when using products that emit VOCs. [2]
Are people who work with oils at risk?
Case reports describe skin allergy in aromatherapists. [6] We found no workplace air limits for essential oil vapors.
Does tap water change what a diffuser emits?
In one test with eucalyptus oil, fine-particle emission was about fivefold higher with tap water than with deionized water. [1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Mixed views on risk
- NAHA (a US professional association) says inhalation presents a very low level of risk to most people. [3] It adds that the only likely risk would be prolonged exposure of perhaps an hour or more to relatively high vapor levels, which could cause headaches, vertigo, nausea and lethargy. [3] This is an association's opinion, quoting two authors.
- NAHA tells practitioners to make sure the treatment room has good ventilation. [3]
- A 2019 study of 14 volunteers with seasonal asthma linked higher outdoor levels of pinene, camphor, linalool and linalyl acetate to respiratory symptoms. [4] It measured plant gases in outdoor air, not diffusers.
- Poison Control says vaporizer products with essential oils, usually camphor, are usually safe when used as directed. [5]
Who should ask a clinician
References
- Volatile organic compound and particulate matter emissions from an ultrasonic essential oil diffuser, Schwartz-Narbonne H et al., Indoor Air 2021, PMID 33905580. Read 2026-10-23.
- Volatile Organic Compounds' Impact on Indoor Air Quality, US Environmental Protection Agency. Read 2026-10-23.
- Safety, National Association for Holistic Aromatherapy (NAHA, US professional association); page undated; the eye-safety section is an article by the aromatherapy educator Robert Tisserand. Read 2026-10-23.
- Essential oils, asthma, thunderstorms, and plant gases: a prospective study of respiratory response to ambient biogenic volatile organic compounds (BVOCs), Gibbs JE, J Asthma Allergy 2019, PMID 31417289. Read 2026-10-23.
- Essential oils: Poisonous when misused, Poison Control (US). Read 2026-10-23.
- Allergic contact dermatitis following exposure to essential oils, Bleasel N et al., Australas J Dermatol 2002, PMID 12121401. Read 2026-10-23.