Scented wax melts are often marketed as a safer, cleaner alternative to traditional candles. With no flames or smoke, they seem like the perfect way to make your home smell great without the health risks. However, a new study published in Environmental Science & Technology Letters challenges that perception, revealing that these popular home fragrance products can actually be a major source of indoor air pollution.
The research team, led by scientists from Purdue University, conducted real-world tests in a full-sized residential test house. They found that when scented wax melts are heated, they release high levels of terpenes—fragrant chemicals that react with indoor ozone. This reaction triggers something called new particle formation (NPF), which produces a large number of tiny airborne nanoparticles.
These particles are so small that they can reach deep into the lungs when inhaled—and the quantities produced by wax melts were comparable to those from burning scented candles, using gas stoves, or even from diesel engine exhaust. In fact, the levels measured during wax melt use were among the highest ever recorded indoors for non-combustion sources.
The researchers also found that the dose of these particles deposited in the respiratory tract was similar to exposures near busy roads or during indoor cooking. What’s more, some of these nanoparticles can cross into the bloodstream and may affect other organs, including the brain and liver.
This study highlights an important and surprising fact: just because a product doesn’t burn doesn’t mean it’s pollution-free. While more research is needed to understand the health impacts of these particles, the authors suggest that consumers and manufacturers alike should rethink the assumed safety of flame-free aromatherapy products.
Reference:
Patra, S. S., Jiang, J., Liu, J., Steiner, G., Jung, N., & Boor, B. E. (2025). Flame-Free Candles Are Not Pollution-Free: Scented Wax Melts as a Significant Source of Atmospheric Nanoparticles. Environmental Science & Technology Letters, 12(2), 175–182. https://doi.org/10.1021/acs.estlett.4c00986
Serra Húnter Fellow of Sociology at Universitat Rovira i Virgili.
Former DAAD-Gastprofessorin at Julius-Maximilians-Universität Würzburg