Source · product
Air fresheners
Part of: Cleaning products
Also: fragrance diffusers, scented products, plug-in fresheners
Products that add fragrance to a room — sprays, plug-ins, gels, diffusers and scented candles. They do not remove anything from the air; they release volatile organic compounds, mainly terpenes, which react with ozone indoors to form formaldehyde and secondary particles.
Why it matters indoors
The name describes an intention, not a mechanism. An air freshener adds substances to the air; it removes none. Masking an odour with fragrance leaves the source of the odour in place — usually dampness, cooking residues or an unventilated room — and adds a second emission on top of the first.
What they emit
Fragrance formulations are dominated by terpenes such as limonene and pinene, together with alcohols, esters and, in some products, aldehydes. Screening studies of air fresheners and of fragrance diffusers find dozens of individual volatile organic compounds per product, and the emission is continuous in plug-ins and diffusers rather than episodic as in a spray. Labelling rarely names the individual compounds, because fragrance mixtures are treated as proprietary.
The reaction that matters
Terpenes react readily with ozone, which enters from outdoors or is produced by some appliances. The products of that reaction include formaldehyde and ultrafine secondary organic aerosols that form in the room itself. That is the reason the topic gets attention out of proportion to the emission rate: the substance measured afterwards is not the one that was released.
Who is sensitive
People who report headache, eye irritation or airway symptoms in scented rooms, and people with asthma. Reported intolerance to fragranced products is common enough in surveys to matter in a shared workplace, where one person’s plug-in is everyone’s exposure.
What to do instead
Remove the source of the odour and ventilate. Where a scent is wanted, an episodic release in a ventilated room is a smaller exposure than a continuous one in a closed room, and it is worth keeping fragrance away from bedrooms, where exposure lasts all night.
What the studies report
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Formaldehyde (CH₂O) | beta 0.56 (0.30–0.81) | — · office | cross-sectional study of 261 office workers: indoor formaldehyde measured in the offices and related by multiple linear regression to the equipment and products used there, among them printers, photocopiers, glue, liquid paper, air fresheners and cleaning agents | F-1372 Investigating exceedances of formaldehyde levels and source … (2024) | machine |
| — | prevalence 20.4 | general population | nationally representative survey of the general population of the United States (n = 1,136) about health problems attributed to fragranced consumer products, including air fresheners, deodorisers and scented cleaning products | F-1373 Steinemann Fragranced consumer products: exposures and effects from emi… (2016) | machine |
| — | prevalence 17.5 | general population | nationally representative survey of the general population of the United States (n = 1,136) about health problems attributed to fragranced consumer products, including air fresheners, deodorisers and scented cleaning products | F-1375 Steinemann Fragranced consumer products: exposures and effects from emi… (2016) | machine |
| Limonene | other 159 | — · classroom | measurement campaign in school buildings: volatile organic compounds sampled in 144 school rooms and 35 outdoor locations across conventional, EnergyStar and LEED schools, with walk-through surveys recording the sources present in each room | F-1589 Zhong et al. Volatile Organic Compounds (VOCs) in Conventional and High P… (2017) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. Rows are re-checked by a person over time. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
In the literature
- Steinemann Ten questions concerning air fresheners and indoor built environments (2016). Building and Environment. doi:10.1016/j.buildenv.2016.11.009 CKB 0142
- Volatile organic compounds in air fresheners and their potential impacts on indoor air quality (2012). CKB 0128
- Cheng et al. Volatile organic compound emissions from indoor fragrance diffusers. Atmosphere. doi:10.3390/atmos14061012 CKB 0241
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.
Cite this page
Coridum Research. Air fresheners. Coridum Knowledge G-0096, 16 September 2026. https://coridum.com/k/G-0096/