A new research found that aroma compounds released from the scented wax melts can react with ozone in indoor air to form potentially toxic particles. This challenges the belief that scented wax melts are safer than combustion-based candles. The study was published in the ACS’ Environmental Science & Technology Letters.
There have been previous researches that have shown that scented wax melts emit more airborne scent compounds than traditional candles. According to the new study, the direct heating of the wax maximises its surface area which releases more fragrance such as volatile organic compounds (VOCs) made of hydrocarbons – into the air.
Researchers know that these chemicals can react with other compounds in the air to form nanometer-wide particles which have been linked to negative health effects when inhaled. However, the potential for nanoparticle formation during wax-melt use was unknown.
So, Nusrat Jung, Brandon Boor and colleagues from Purdue University in the US set out to investigate this process using wax melts in a full-scale house model that mimicked a typical residential house. The researchers conducted experiments on 15 commercially available wax melts, both unscented and scented ( 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.
The researchers said, "These particles could pose an inhalation risk because they are small enough to pass through respiratory tissues and enter the bloodstream."
The team also calculated that a person could inhale similar amounts of nanoparticles from wax melts as from traditional candles and gas stoves.
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.