Certainly, gas stoves and heaters can cause indoor air pollution, with carbon monoxide (CO) being the main risk. Even if you have a CO alarm, the level at which it will go off is usually the “this will kill you tonight if you don’t do something about it soon” level, rather than the “this will slowly kill your brain cells but you’ll keep functioning otherwise, until one day you don’t” levels of CO.

Still, do by all means have a CO alarm if you have anything in your house that can release CO!

See also: Association Between Carbon Monoxide Intoxication and Incidence of Ischemic Stroke: A Retrospective Nested Case-Control Study in South Korea

Fun fact about those stoves:

❝Just 1 kilogram of cooking fuel emits 10 quadrillion particles smaller than 3 nanometers, which matches or exceeds what’s emitted from cars with internal combustion engines.

At that rate, you might be inhaling 10-100 times more of these sub-3 nanometer particles from cooking on a gas stove indoors than you would from car exhaust while standing on a busy street.❞

~ Ka‌yla Alb‌ert

But today, we’re not here about that

Rather, we are looking at some more innocent-seeming things, such as scented cleaning products and air fresheners. Notably, the biggest problem is often not even the cleaning chemicals themselves. Of course: please don’t breathe bleach fumes, etc.

But that’s an obvious risk, and today we’re about the less obvious risks.

So… What is the less obvious risk here?

It’s the fragrances. The terpenes used to hold them react with ozone in the air, to create new nanoparticles. And, just like the nanoparticles from the stove, these can reach very high concentrations indoors, and suffice it to say, if you can smell the fragrance then you have the pollutants inside you.

You can read about how badly different products score, here:

Rapid Nucleation and Growth of Indoor Atmospheric Nanocluster Aerosol during the Use of Scented Volatile Chemical Products in Residential Buildings ← you’ll need to scroll down to the table with different cleaning products and air fresheners

Further, the seemingly-harmless scented candle is, as it turns out, quite a menace too:

❝Full-scale emission experiments were conducted in the Purdue zEDGE Test House using a variety of scented candles (n = 5) and wax warmers/melts (n = 14) under different outdoor air exchange rates (AERs). Terpene concentrations were measured in real-time using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). PTR-TOF-MS measurements revealed that scented candle and wax warmer/melt products emit a variety of monoterpenes (C₁₀H₁₆) and oxygen-containing monoterpenoids (C₁₀H₁₄O, C₁₀H₁₆O, C₁₀H₁₈O, C₁₀H₂₀O), with peak concentrations in the range of 10⁻¹ to 10² ppb. Monoterpene EFs were much greater for scented wax warmers/melts (C₁₀H₁₆ EFs ∼ 10² mg per g wax consumed) compared to scented candles (C₁₀H₁₆ EFs ∼ 10⁻¹ to 10⁰ mg per g wax consumed). Significant emissions of reactive terpenes from both products, along with nitrogen oxides (NO, NO₂) from candles, depleted indoor ozone (O₃) concentrations. Terpene iFs were similar between the two products (iFs ∼ 10³ ppm) and increased with decreasing outdoor AER. Terpene iFs during concentration decay periods were similar to, or greater than, iFs during active emission periods for outdoor AERs ≤ 3.0 h⁻¹.

Overall, scented wax warmers/melts were found to release greater quantities of monoterpenes compared to other fragranced consumer products used in the home, including botanical disinfectants, hair care products, air fresheners, and scented sprays.❞

~ Dr. Emily Reidy et al.

Read in full: Rapid Nucleation and Growth of Indoor Atmospheric Nanocluster Aerosol during the Use of Scented Volatile Chemical Products in Residential Buildings

Put in fewer words: scented candles are bad, and wax melts (the kind with no flame, that one might easily expect to thus produce fewer emissions) are at least as bad if not worse, and both are even worse than cleaning products.

Some of the same research team conducted further studies, because of this this, finding:

❝We performed field measurements in a residential test house to investigate atmospheric nanoparticle formation from scented wax melt use. We employed a high-resolution particle size magnifier-scanning mobility particle sizer (PSMPS) and a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) for real-time monitoring of indoor atmospheric nanoparticle size distributions and terpene mixing ratios, respectively.

Our findings reveal that terpenes released from scented wax melts react with indoor atmospheric ozone (O₃) to initiate new particle formation (NPF) events, resulting in significant indoor atmospheric nanoparticle concentrations (>10⁶ cm^–3) comparable to those emitted by combustion-based scented candles, gas stoves, diesel engines, and natural gas engines.

We show that scented wax melt-initiated NPF events can result in significant respiratory exposures, with nanoparticle respiratory tract deposited dose rates similar to those determined for combustion-based sources.

Our results challenge the perception of scented wax melts as a safer alternative to combustion-based aromatherapy❞

~ Dr. Satya Patra et al.

Read in full: Flame-Free Candles Are Not Pollution-Free: Scented Wax Melts as a Significant Source of Atmospheric Nanoparticles

In short: you might want to ditch the fragranced products!

Want to do more?

Give your household hair a makeover with this multi-vector approach to deal with different risks:

What’s Lurking In Your Household Air?

For that matter, the air is a very important factor for the health of your lungs (and thus, for the health of everything that’s fed oxygen by your lungs), and there are more things we can do in that regard as well:

Seven Things To Do For Good Lung Health!

Take care!