Late summer gives us one of the simplest pleasures of owning a home: turning off the air conditioning, opening the windows and letting fresh air move through the house. It is also a time when many of us clean with those windows wide open - wiping counters, mopping floors and leaving behind the familiar scent of lemon, pine or lavender. For generations, that fragrance has become shorthand for something reassuring: the house is clean.
But what if the smell we associate with cleanliness is not necessarily evidence of clean air?
New research presented August 27 at the fall meeting of the American Chemical Society offers homeowners a surprisingly practical reason to rethink heavily scented cleaning products. Researchers led by Brandon Boor at Purdue University found that fragrance compounds released by both conventional cleaners and botanical or essential-oil-based products can react with ozone already present in indoor air. Within minutes, those reactions can create enormous numbers of ultrafine airborne particles - pollution that is invisible to the eye and small enough to travel deep into the respiratory system.
The encouraging part is that this is not a home problem requiring a contractor, a renovation or an expensive piece of equipment. It is something nearly every homeowner can address immediately.
What Is Happening in the Air?
Many familiar fragrances in household cleaners come from a family of compounds called terpenes. Limonene provides a citrus scent. Pinene smells like pine. Linalool is associated with lavender, and thymol with thyme. These compounds occur naturally in plants, which is one reason products containing them can sound reassuringly "natural." But natural compounds still participate in chemistry.
When scented cleaners are sprayed, wiped or mopped onto surfaces, some of those fragrance compounds evaporate into the room. If they encounter ozone, chemical reactions can produce new airborne particles. Purdue's researchers observed particle formation beginning within minutes. During cleaning, airborne terpene concentrations could reach tens to hundreds of times the concentrations found naturally in a forest.
That does not mean cleaning your kitchen is the same health exposure as standing beside a busy highway. The Purdue team reported that the estimated respiratory dose of these particles could rival or exceed the particle dose near traffic, but the particles are chemically different. The research should be understood as a reason to reduce unnecessary exposure - not a reason to stop cleaning.
The 'Natural' Cleaning Trap
One of the more useful lessons for homeowners is that "botanical," "plant-based" or "made with essential oils" does not automatically mean a product is neutral from an indoor-air standpoint. The Purdue experiments included both conventional scented products and botanical products. If a product releases reactive fragrance compounds into indoor air, the chemistry can occur regardless of how the fragrance was marketed.
This is an important distinction because surface cleanliness and air cleanliness are not the same thing. A product can do an excellent job removing dirt or microbes from a countertop while simultaneously adding volatile compounds to the air.
Five Easy Things Homeowners Can Do
1. Choose fragrance-free or low-fragrance products when practical. Cleaning does not require a lingering perfume. Reducing the source is generally the most effective way to reduce an indoor pollutant.
2. Open the windows while cleaning - when the outdoor air is clean. This is especially easy during late summer and early fall. Ventilation helps dilute and exhaust pollutants produced indoors. If outdoor smoke, high ozone or other pollution is elevated, however, keeping windows closed may be the better choice.
3. Use exhaust fans that vent outdoors. Kitchen and bathroom exhaust fans can help remove pollutants near where they are generated rather than allowing them to disperse throughout the house.
4. Avoid stacking fragrances. Using several strongly scented sprays, wipes, floor cleaners and air fresheners during the same cleaning session can increase the amount of fragrance chemistry occurring indoors.
5. Avoid devices that intentionally generate ozone. EPA advises against ozone generators in occupied spaces. Ozone is itself a lung irritant and can also react with fragrance compounds to create additional pollutants.
Fresh Air Before Fancy Equipment
The larger Healthy Homes lesson is wonderfully uncomplicated. Improving indoor air does not always require purchasing something. EPA's basic hierarchy begins with source control - reduce or remove the thing creating pollution - followed by ventilation with clean outdoor air. Filtration can be an excellent supplement, but it should not become a substitute for controlling unnecessary sources in the first place.
So as the days cool and the windows begin staying open again, consider changing one small habit. The next time the house is cleaned, use less fragrance, turn on the exhaust fan and let clean outdoor air move through when conditions allow.
We have been trained to think that lemon, lavender and pine are the smell of a clean house. Perhaps the healthier goal is simpler.
Maybe the healthiest smell of a freshly cleaned house is no smell at all.
Sources & Further Reading
• American Chemical Society. “Scented cleaning products create invisible air pollution.” Science release, August 27, 2026. Research presented at ACS Fall 2026 by Purdue University researchers.
• U.S. Environmental Protection Agency. “Improving Your Indoor Environment.” Guidance includes minimizing indoor use of cleaners, perfumes and other household chemical products and ventilating while cleaning.
• U.S. Environmental Protection Agency. “Guide to Air Cleaners in the Home.” EPA recommends source control and ventilation with clean outdoor air as primary indoor-air strategies and advises avoiding air cleaners that intentionally produce ozone.
• U.S. Environmental Protection Agency. “Sources of Indoor Particulate Matter (PM).” EPA notes that pine- and citrus-scented cleaning products and fragrances can react with ozone to form particulate matter indoors.