Scented Wax Melts Create Particles in Indoor Air That ‘You Shouldn’t Be Breathing In’: 'Comparable to Diesel Engines'

Main Article: https://people.com/scented-wax-melts-create-particles-you-shouldn-t-breathe-in-11681024

Scientific Study: https://pubs.acs.org/doi/10.1021/acs.estlett.4c00986

Fig. 1. The figure shows a wax warmer setup with wax melting in the center. (Image obtained from https://gardentherapy.ca/herbal-wax-melts/) 

    Atmospheric nanoparticles are tiny particles or droplets suspended in the air, typically measuring less than 100 nanometers in diameter. These particles originate from both natural sources, such as sea spray, volcanic eruptions, and wildfires, and human-made sources like vehicle emissions, industrial processes, and fossil fuel combustion. Due to their small size and large surface area, atmospheric nanoparticles play a significant role in climate dynamics and human health. They can influence cloud formation, affect the Earth's balance by scattering and absorbing sunlight, and contribute to the formation of acid rain. 

    Aerosol chemistry refers to the complex interactions between these particles and gases in the atmosphere. Aerosol particles can undergo chemical reactions with water vapor, sulfur dioxide, nitrogen oxides, and other pollutants, producing secondary aerosols and contributing to smog and particulate matter that can harm respiratory systems. Studying the chemistry of aerosols is essential for understanding their environmental and health impacts, as well as their role in atmospheric processes like cloud formation and climate change. Aromatherapy is a well-known trend that has taken the world by storm, and essential oils are the primary source of the scents used. These essential oils are typically comprised of concentrated chemical extracts from plants; chemicals like terpenes will be talked about later in the scientific study. Many different diffusion methods exist for these oils, such as candles, wall scents, and wax melts. 

    In an article posted by People Magazine, the author highlights the dangers of scented wax melts. A recent study published in Environmental Science & Technology Letters has revealed that scented wax melts can generate indoor air pollution levels comparable to those produced by diesel engines. The research indicates that terpenes (the chemical compounds responsible for the fragrances in wax melts) react with existing ozone in indoor environments, forming significant particulate pollution. This finding suggests that while wax melts may seem like a healthier alternative to scented candles, they can still contribute substantially to indoor air pollution. The study emphasizes the importance of indoor air quality in building design and HVAC system operations to mitigate potential health risks associated with such pollutants.

    The study published in Environmental Science & Technology Letters was conducted by a research group from Purdue University. In this study, they simulated a "test house" to replicate most modern homes. Several instruments were utilized to demonstrate secondary aerosol formation, including a high-resolution particle size magnifier-scanning mobility particle sizer (PSMPS) and a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). It was found that the terpenes released by max melts are comparable to those released by candles, gas stoves, and diesel engines. Specifically, the terpenes are said to react with atmospheric ozone and initiate new particle formation that increases nanoparticle concentrations by 10^6 cm-3. This challenges the claim that wax melts pose less threat than combustion-based aromatherapy. 

Fig. 2. (a) Representative time-resolved evaluation of indoor atmospheric nucleation and growth (NPF) during the use of bergamot-scented wax melts (two cubes) in the Purdue zEDGE test house at two different outdoor air ventilation rates [kvent values of 3.0 h−1 (top) and 6.5 h−1(bottom)]. (b) Relationship between the effective terpene ozonolysis rates [Keff·(MT + MTD)·O3] and particle nucleation rates at the critical diameter (J1.75) (left y-axis), along with mean condensational growth rates for particles in the size range of 3 nm < dem < 10 nm (right y-axis) during NPF events initiated by scented wax melts. Legend: zEDGE6.5, scented wax melts used in the zEDGE test house at a kvent of 6.5 h−1; zEDGE3.0, scented wax melts used in the zEDGE test house at a kvent of 3.0 h−1; CLOUDa, particle nucleation rates (J1.7) from ref 24; AURAb, particle nucleation rates (J1.7) from ref 28; CLOUD c, particle nucleation rates (J1.7) from ref 29; CLOUDd, apparent particle growth rates (3.2 nm < dem < 8nm) from ref 30. (c) Comparison of size-integrated sub-10 nm atmospheric nanoparticle number concentrations from scented wax melt use (this study) vs. scented candle combustion (ref 31), gas stove combustion (Gas Stove a, indoor bulk air measurements from ref 12; Gas Stoveb, cookstove emissions hood measurements from ref 32), diesel engine (exhaust emission measurements at 75% engine load from ref 33), and natural gas engine(exhaust emission measurements, where the value represents the mean, calculated from the engine operating under both lower- and higher-torque conditions, from ref 34). The error bars for this study and for Gas Stove-a represent the 25th and 75th percentile values, whereas for the diesel engine, they represent the values at 50% and 100% engine loads. For the natural gas engine, the error bars correspond to the values under lower and higher-torque operating conditions. (Pulled from Environmental Science & Technology Letters pubs.acs.org/journal/estlcu Letterhttps://doi.org/10.1021/acs.estlett.4c00986Environ. Sci. Technol. Lett. 2025, 12, 175−182176)

    The most important issue this study highlights is the unexpected and significant impact of scented wax melts on indoor air quality.  This poses potential health risks, especially in poorly ventilated indoor environments, as inhaling fine particulate matter has been linked to respiratory and cardiovascular issues. The study, however, lacks the need for greater awareness of indoor air pollution sources and improved ventilation strategies to mitigate these risks. It brings to question what other commonly used aerosols are used in poorly ventilated areas. Or, as an even greater worry, how much of these newly formed particles are being released into our atmosphere. 

    The People Magazine article does a great job of taking all this information and picking out the main components. However, it lacks a more extensive discussion of the study's implications. It goes through how the study was conducted and the conclusions drawn. Still, it mostly glosses over all the important data to support these claims and, more importantly, what they could mean for the overall health of people and our environment. 

    I would give this article a 6 out of 10, mainly due to the short length and being primarily comprised of direct quotes. In my opinion, this article is a super easy read and has an eye-catching title. It does a great job of explaining the chemistry behind terpenes and gives an easy-to-understand layout of how the study was conducted. It mentions possible solutions for all of these added particles, such as adding HVAC systems into building design. It further helps the issue of aerosols and how they can affect our environment. This could lead people to look more into aerosols and their potential impacts on human and atmospheric health.