Measurements from 112 London residences found incense and oil diffusers could account for nearly half of bedroom PM2.5 exposure in homes where they were used, with the highest pollution occurring in smaller, poorly ventilated dwellings.
By yourNEWS Media Newsroom.
Common products used to make homes smell pleasant can become major sources of indoor fine-particle pollution, with incense, oil diffusers and candles producing sharp increases in PM2.5 concentrations during everyday household use, according to new research conducted in London.
The study, published in the September 2026 edition of Environment International, monitored 112 occupied London homes between 2022 and 2024 rather than testing the products solely under controlled laboratory conditions. Researchers used high-time-resolution pollution measurements and methods designed to distinguish indoor pollution sources as residents followed their normal routines.
The highest hourly PM2.5 concentrations associated with fragrance use reached 1,293 micrograms per cubic meter for incense, 858 micrograms per cubic meter for oil diffusers and 622 micrograms per cubic meter for candles.
Those short-lived peaks should not be directly equated with the World Health Organization’s 24-hour PM2.5 guideline because one represents an hourly concentration while the other is based on an entire day’s average. They nevertheless demonstrate how sharply indoor particle levels could rise when the products were used.
The study found the effect extended beyond isolated pollution spikes.
Among households using incense, the product accounted for nearly half of measured bedroom PM2.5 exposure. Oil diffusers produced a similarly large contribution in households where they were used, while candles accounted for approximately 14% of bedroom exposure.
Incense produced the greatest overall indoor pollution burden. Environmental Health News reported that homes burning incense had average indoor PM2.5 concentrations nearly three times the outdoor levels measured for those households.
Researchers also found that the WHO’s 24-hour PM2.5 guideline of 15 micrograms per cubic meter was frequently exceeded.
Among homes using candles, the median household exceeded that guideline on approximately 40% of monitored days. In some households using incense, concentrations exceeded the guideline on most of the days monitored.
The effect was not uniform across homes.
Smaller residences and rooms with inadequate ventilation experienced the greatest exposures, according to the researchers. The finding may become increasingly important as buildings are constructed or renovated to retain more energy and outside air exchange declines unless ventilation systems are specifically designed to compensate.
“This study demonstrates that fragrance products are a substantial yet underrecognized driver of indoor particulate pollution,” a researcher stated. “Our findings show that routine fragrance practices can substantially reshape indoor exposures.”
The findings are noteworthy because incense and candles involve obvious combustion, while oil diffusers do not necessarily appear to users to be sources of particulate pollution.
Burning almost any material can produce particulate matter. The U.S. Environmental Protection Agency identifies candles as an indoor source of PM and recommends adequate ventilation when candles or incense are burned indoors. Indoor particles can also originate from cooking, smoking, fireplaces, heaters, printers and outdoor pollution that enters through windows, doors and other openings.
The London study suggests fragrance products can become a particularly important source under certain household conditions.
Fine particulate matter consists of particles with aerodynamic diameters of 2.5 micrometers or less. Because of their extremely small size, the particles can penetrate deeply into the lungs, while some can enter the bloodstream.
The WHO identifies PM2.5 among the air pollutants with the strongest evidence of adverse health effects, along with PM10, ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. Long-term and repeated exposure to particulate pollution is associated with cardiovascular and respiratory disease, stroke, chronic obstructive pulmonary disease and lung cancer.
The new research measured pollution exposure rather than medical outcomes. It did not track whether people using candles, incense or diffusers subsequently developed heart disease, cancer, asthma or other illnesses.
That distinction is important: the study demonstrates that routine fragrance use can substantially alter indoor PM2.5 concentrations but does not establish that the particular exposures measured in the participating homes caused disease.
The broader health burden attributed to air pollution, however, is substantial.
The WHO currently estimates that the combined effects of ambient and household air pollution are associated with approximately 7 million premature deaths worldwide each year, primarily through cardiovascular disease, stroke, chronic respiratory disease, lung cancer and acute respiratory infections.
A newer WHO technical summary lists air pollution as the world’s leading environmental health risk factor and places the estimated annual burden at approximately 6.6 million deaths, depending on the dataset and methodology used.
Earlier WHO figures cited in environmental health literature estimated that roughly nine in 10 people worldwide breathed air containing pollutant concentrations above recommended levels. Current WHO information places the proportion at approximately 99% of the global population for exposure above its guideline level for fine particulate matter.
Other often-cited mortality estimates have also changed as methods and exposure data have improved. A major 2017 Lancet Commission report estimated that pollution of all types was responsible for approximately 9 million premature deaths in 2015, representing about 16% of deaths worldwide at the time. Those figures concern pollution broadly and should not be interpreted as deaths specifically caused by scented household products.
Environmental Health News, which summarized the fragrance study in September, cited an estimate of 6.6 million deaths attributable to air pollution in 2019 while describing the household findings as evidence of a comparatively understudied source of personal exposure.
“The results of this study point to the underexamined role of commonplace products as sources of at-home exposures,” the Environmental Health Sciences report stated.
Researchers have additional reasons to examine fragrance products beyond the PM2.5 measured in the London study.
Fragrance formulations can contain numerous chemicals, and complete chemical identities are not always apparent to consumers. Some fragrance formulations are treated as proprietary mixtures or contain components protected as trade secrets.
The EPA’s Safer Choice program, which evaluates chemicals and product formulations against health and environmental criteria, maintains separate standards for fragrance ingredients. The program excludes listed carcinogens, mutagens, reproductive and developmental toxicants, persistent and bioaccumulative toxic compounds and listed respiratory sensitizers from fragrances used in qualifying Safer Choice products.
EPA documentation also recognizes that fragrance formulas may contain proprietary information protected as trade secrets, although disclosure requirements vary according to the product and regulatory program involved.
That issue is distinct from the principal finding of the London research. Gao and colleagues focused specifically on fine particulate exposure generated during actual household fragrance use rather than attempting to establish the toxicological effects of every chemical ingredient in the products.
The study’s residential design provides another important distinction.
Laboratory experiments can determine how much pollution a product emits under standardized conditions, but actual exposure in a home depends on factors including room volume, ventilation, frequency and duration of product use and pollution entering from outdoors.
By monitoring occupied homes, researchers were able to observe how those variables influenced what residents actually breathed.
“This study demonstrates that fragrance products are a substantial yet underrecognized driver of indoor particulate pollution…. Our findings show that routine fragrance practices can substantially reshape indoor exposures.”
The finding that pollution accumulated most strongly in compact or inadequately ventilated dwellings also raises questions about efforts to make buildings increasingly airtight for energy efficiency.
The authors said the results provide evidence relevant to ventilation design and assessments of Net Zero housing, particularly when indoor pollution sources are considered alongside efforts to reduce energy loss.
For consumers seeking to reduce indoor PM2.5, eliminating or reducing the source is generally more effective than attempting to remove pollution after it has already entered the air.
The EPA specifically advises reducing indoor particulate sources where practical and says adequate ventilation should be provided when candles and incense are burned. During periods when outdoor wildfire pollution is high, the agency goes further and recommends avoiding candles and incense indoors because they add more particles to already polluted indoor air.
Ventilation can reduce pollutants generated indoors when outdoor air is relatively clean, while properly sized particle filtration can help remove suspended PM2.5. The appropriate strategy depends on outdoor conditions: opening windows during heavy wildfire smoke or severe outdoor pollution, for example, can increase rather than decrease indoor particle exposure.
The findings therefore do not mean that every occasional candle or diffuser creates the same exposure or health risk. Pollution concentrations varied among homes, and the study did not establish a threshold at which use of a particular fragrance product produces a specific disease.
What the measurements show is that products generally associated with atmosphere or fragrance can, under routine real-world conditions, become major sources of the fine particles people breathe inside their homes.
The authors concluded that indoor air-quality strategies should account for those sources, particularly in smaller and increasingly airtight residences where pollutants can accumulate more readily.
Additional independent health and environmental reporting, including coverage of household chemical exposures, is available through NaturalNews.com.
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