Study Finds Scented Candles May Emit Potentially Toxic Indoor Particles

New Delhi: Researchers at Purdue University have raised new concerns about the safety of scented wax melts used for indoor fragrance. In a study published in ACS’ Environmental Science & Technology Letters, scientists discovered that aroma compounds emitted from these wax melts can react with ozone in indoor air to form nanoparticles that may pose potential health risks.

Often marketed as a safer alternative to traditional, combustion-based candles, scented wax melts are thought to release fewer pollutants. However, the study challenges this perception. The researchers found that the process of directly heating the wax increases its surface area, leading to the release of higher concentrations of volatile organic compounds (VOCs). In particular, terpenes such as monoterpenes and monoterpenoids are emitted. When these compounds react with ozone, they form sticky substances that aggregate into nanoscale particles ranging from 1 to 100 nanometers in diameter. The concentration of these nanoparticles was comparable to levels previously reported for traditional candles.

To investigate this phenomenon, the research team conducted experiments in a full-scale house model that simulated a typical residential environment. They tested 15 commercially available wax melts, including both unscented and scented varieties—flavors such as lemon, papaya, tangerine, and peppermint were included. The team first established baseline levels of indoor air pollutants before activating the wax warmer for about two hours. Continuous air sampling a few meters away from the wax melts revealed significant levels of airborne nanoparticles.

According to the researchers, these nanoparticles pose an inhalation risk because their small size allows them to pass through respiratory tissues and enter the bloodstream. Calculations based on literature data indicated that exposure to nanoparticles from wax melts may be similar to that from traditional candles and even gas stoves. Notably, when an unscented wax melt was warmed, no terpene emissions or nanoparticle formation were observed, suggesting that the added aroma compounds play a key role in this reaction.

While further toxicology research is needed to fully assess the risks, these findings call for a reevaluation of the safety of scented wax melts for indoor use. The study urges a fresh look at indoor air quality risks.