Serious Health Risks: Scented Wax Melts May Emit Harmful Nanoparticles

Scented wax melts can form potentially harmful nanoparticles when their aroma compounds react with ozone, challenging their reputation as a safer alternative to candles.

Traditional candles can contribute to indoor air pollution by releasing volatile compounds and smoke, which may pose inhalation risks. Scented wax melts are often promoted as a safer alternative since they do not produce flames or smoke. However, a study published in ACS’ Environmental Science & Technology Letters reveals that aroma compounds released from melted wax can react with indoor ozone, forming potentially harmful airborne particles.

Previous research has shown that scented wax melts emit more fragrance compounds than traditional candles. This is because direct heating increases the wax’s surface area, releasing a higher concentration of volatile organic compounds (VOCs), which consist of hydrocarbons.

Scientists already know that these VOCs can interact with other airborne chemicals to produce ultrafine particles, which have been linked to negative health effects when inhaled. However, whether this process occurs during wax-melt use was previously unknown. To investigate, researchers Nusrat Jung, Brandon Boor, and their team studied wax melts in a full-scale house model designed to replicate typical indoor environments.

Testing Air Quality in a Simulated Home

The researchers conducted experiments on 15 commercially available wax melts, both unscented and scented (e.g., lemon, papaya, tangerine, and peppermint), in the model house. They first established a baseline of indoor air pollutants and then switched on the wax warmer for about 2 hours.

During and after this period, the researchers continuously sampled the air a few yards (meters) away from the wax melts and found airborne nanoparticles, between 1 and 100 nanometers wide, at levels that were comparable to previously reported levels for traditional, combustion-based candles. These particles could pose an inhalation risk because they are small enough to pass through respiratory tissues and enter the bloodstream, say the researchers.

Comparing Wax Melts to Other Household Sources of Nanoparticles

Additionally, using literature data, the team calculated that a person could inhale similar amounts of nanoparticles from wax melts as from traditional candles and gas stoves. Previous studies have found exposure to high levels of nanoparticles in indoor air can be linked to health risks like decreased cognitive function and increased prevalence of childhood asthma.

In the experiments, the main VOCs emitted from the wax melts were terpenes, such as monoterpenes and monoterpenoids. The researchers identified that the airborne terpenes reacted with ozone and formed sticky compounds, which aggregated into nanoscale particles. However, after warming an unscented wax melt, the team observed no terpene emissions or nanoparticle formation, which suggests that these aroma compounds contribute to nanoparticle formation.

The researchers say this study challenges the perception that scented wax melts are a safer alternative to combustion-based candles; however, they emphasize that more toxicology research is needed on the risks of breathing in nanoparticles formed from wax melts.

Reference: “Flame-Free Candles Are Not Pollution-Free: Scented Wax Melts as a Significant Source of Atmospheric Nanoparticles” by Satya S. Patra, Jinglin Jiang, Jianghui Liu, Gerhard Steiner, Nusrat Jung and Brandon E. Boor, 3 February 2025, Environmental Science & Technology Letters.
DOI: 10.1021/acs.estlett.4c00986

The authors acknowledge funding from the National Science Foundation; Purdue University; and the American Society of Heating, Refrigerating, and Air Conditioning Engineers.

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