What Science Says About Scented Candles, Wax Melts, and Plug-Ins

Candles, wax melts, and plug-in air fresheners promise cozy ambiance, relaxation, and that "just-cleaned" scent. Television commercials ensure us that it is a simple way to create the perfect home and judging by the common presence of them in many homes, we have believed the marketing pitch.

But what do we really know about what's floating in the air when we light a candle or plug in an air freshener?

Concerns about indoor air quality from fragranced products aren't new. Many of us have long suspected that what makes our homes smell good might not actually be good for us.

I saw a social media post that said a new study from Purdue University claimed scented wax melts can release nanoparticles at levels comparable to diesel exhaust and gas stoves.

My first thought was: Wow! That sounds rather dramatic. Is it true? And, if it is, what does it really mean for our health - and for the pets and kids who share our homes?

Let's dig into the science, cut through the hype, and look at safer choices for people and dogs alike.

What the Purdue Study Found

A new Purdue University study published in Environmental Science & Technology Letters looked specifically at scented wax melts in a realistic home setting (the Purdue zEDGE Test House).

• When heated, scented wax melts released fragrance chemicals (terpenes) into the air.
• Those terpenes reacted with indoor ozone to form new nanoparticles - particles so tiny they can penetrate deep into the lungs.
• Particle levels reached concentrations similar to emissions from combustion sources like gas stoves, candles, and even diesel exhaust (when measured by number of particles, not by toxicity).
• Unscented wax melts produced almost no nanoparticles, pointing to the fragrance additives - not the wax itself - as the problem.

What the Study Did Not Show

While the Purdue findings are important, it's also crucial to understand what the study didn't prove:

• It did not measure health effects such as cancer, infertility, or hormone disruption.
• It did not identify specific chemicals like formaldehyde, benzene, or phthalates in the melts tested.
• It only measured particle numbers and exposure potential, not toxicity or long-term outcomes.

This means the Purdue study by itself doesn't show that using scented candles or wax melts will make you sick. However, other scientific research has already documented the health consequences of chronic nanoparticle and volatile organic compound (VOC) exposure:

• Respiratory and lung disease: Ultrafine particles can penetrate deep into the lungs, where they've been linked to asthma, chronic bronchitis, and reduced lung function (Oberdörster, 2001).
• Cardiovascular impacts: Long-term exposure to fine and ultrafine particles increases the risk of heart disease, arrhythmias, and stroke (Pope & Dockery, 2006).
• Secondary pollutants: When fragrance terpenes react with ozone, they can form formaldehyde and other reactive aldehydes, both of which are respiratory irritants and potential carcinogens (Weschler, 2006).

So while the Purdue study stops after proving particle formation occurs, the wider scientific literature makes it clear why those particles matter for long-term health. This is where the social media claims get tangled - they aren't directly supported by Purdue's data, but they are connected to decades of research on what chronic exposure to ultrafine particles and reactive chemicals can do.

Paraffin vs Soy vs Beeswax Candles

One of the hottest debates is which wax is "safest." Here's what the research shows:

• Paraffin Wax

  • Made from petroleum byproducts.
  • When burned, can release soot and small amounts of benzene/toluene.
  • Still emits VOCs when fragranced - meaning scented paraffin candles can form nanoparticles through the same terpene + ozone chemistry.
  • Indoor impact depends heavily on ventilation.
    
    

• Soy Wax

  • Plant-based, renewable.
  • Burns cleaner with less soot than paraffin.
  • Still emits VOCs when fragranced - meaning scented soy candles can also form nanoparticles through the same terpene + ozone chemistry.
    
    

• Beeswax

  • Natural and long-burning.
  • Emits very little soot.
  • Sometimes promoted as "air-purifying," but scientific evidence for this is weak.
  • Still emits VOCs when fragranced - meaning scented beeswax candles also form nanoparticles through the same terpene + ozone chemistry.

Artificial Fragrances: The Bigger Concern

As you can see from above, whether it's a candle, wax melt, or a plug-in freshener, the biggest risk comes from synthetic fragrances which have links to health impacts. And that is after all, the point of air fresheners.  Nobody ever made an unscented air freshener.

• Fragrance terpenes (limonene, linalool, pinene, etc.) smell pleasant but react with ozone to create secondary pollutants.
• This includes nanoparticles as shown in the Purdue study, but also potentially formaldehyde and other reactive aldehydes (documented in other air chemistry studies).
• Plug-in air fresheners and sprays may be worse, because they continuously release VOCs into indoor air - even when you aren't home.
• Artificial fragrances often contain undisclosed chemical blends (sometimes 50 to 100+ compounds), making it hard to know exactly what you're inhaling and almost certainly posing long term health risk.

Why This Matters for Dogs

It's not just people who are exposed to fragrance-related pollution - our dogs breathe it in too. In fact, they may be even more vulnerable:

• Closer to the ground: Nanoparticles and heavier VOCs can linger low in the air, right where dogs spend most of their time.
• Smaller body size: Dogs have faster breathing rates and smaller lungs than humans, which means pollutants can reach harmful concentrations more quickly relative to their body weight.
• Weaker detox pathways: Dogs metabolize certain chemicals (like some fragrance compounds and phthalates) less efficiently than humans, which can make them more susceptible to bioaccumulation, buildup and toxic effects.
• Chronic exposure: If you use candles, wax melts, or plug-ins daily, your dog is breathing those compounds for hours - often in confined spaces where ventilation is limited.

Veterinarians have raised concerns that chronic exposure to artificial fragrances could contribute to respiratory irritation, allergies, or even long-term health problems in pets. While studies specific to dogs and candles are limited, we know from toxicology research that pets are generally more sensitive to indoor air pollutants than humans.

Safer Choices for a Pet-Friendly Home

• Skip the plug-ins and constant air fresheners - they're a continuous exposure source.
• Use unscented soy based candles if you want visual ambiance and ensure the room is ventilated.
• If you use essential oils, make sure they are high quality, pet-safe essential oils and used in very small amounts using water based, cool mist essential oil diffusers such as ultrasonic options. Remember, you get what you pay for and with essential oils, quality matters.
• Consider alternatives like opening windows to keep your home naturally aired out.
• Always monitor your pet for signs of sensitivity: sneezing, watery eyes, coughing, or avoiding the room when the fragrance is in use. Our dogs are smart! They will tell you when something isn't good for them!

Bottom Line

Purdue proved scented wax melts pump out pollution, and combined with decades of research show those particles can harm your lungs, your heart — and your dog’s health too.

You'd not back a diesel truck into your living room and feel good about breathing that air, much less your dog, so why intentionally create poor air quality even when the danger is hidden behind a warm vanilla scent? 

Ditch the plug-ins, get rid of those scented candles, and crack a window so you and your pets can enjoy the clean, fresh air without poisoning it for the sake of creating a cozy atmosphere. Instead, get an ultrasonic water based diffuser and some pet safe essential oil blends!  You’ll not only create the atmosphere you want but will also enhance the health and wellness of yourself and your dog through the many natural benefits essential oils provide.

References

1. Patra, S. S., Breysse, P. N., Boor, B. E., et al. (2025). Flame-Free Candles Are Not Pollution-Free: Scented Wax Melts as a Significant Source of Atmospheric Nanoparticles. Environmental Science & Technology Letters. PMID:

2. Jetter, J. J., et al. (2002). Characterization of emissions from burning candles. Chemosphere, 46(6), 907-921.

3. Nazaroff, W. W., & Weschler, C. J. (2004). Cleaning products and air fresheners: exposure to primary and secondary air pollutants. Atmospheric Environment, 38(18), 2841-2865.

4. Singer, B. C., et al. (2006). Cleaning products and air fresheners: emissions and exposure. Indoor Air, 16(3), 179-191.

5. Purdue University Newsroom (2025). Air inside your home may be more polluted than outside due to everyday chemical products. Retrieved from Purdue.edu

6. Weschler, C. J. (2006). Ozone's impact on public health: Contributions from indoor exposures to ozone and products of ozone-initiated chemistry. Environmental Health Perspectives, 114(10), 1489-1496.

7. Oberdörster, G. (2001). Pulmonary effects of inhaled ultrafine particles. International Archives of Occupational and Environmental Health, 74(1), 1-8.

8. Pope, C. A., & Dockery, D. W. (2006). Health effects of fine particulate air pollution: lines that connect. Journal of the Air & Waste Management Association, 56(6), 709-742.

9. Weschler, C. J. (2006). Ozone's impact on public health: Contributions from indoor exposures to ozone and products of ozone-initiated chemistry. Environmental Health Perspectives, 114(10), 1489-1496.