Scented candles do a good job of giving closed rooms a fresh, inviting scent. However, they may be giving more than a pleasant aroma - they may be forming harmful substances that can cause cancer, according to research done for the BBC series "Trust Me, I'm a Doctor."
The "Trust Me, I'm a Doctor" team worked with Alastair Lewis from the National Centre for Atmospheric Science and studied the air quality in six houses in York, England, that had similar conditions. An air sampler was placed in each house to determine what chemicals are present and in what amount.
The residents of the six houses were told to write down the products they used. The study was conducted for five days in the month of November, a time when the residents closed their doors and windows more often because of the cold.
At the end of the study period, the chemical found in the highest amounts, particularly in three houses, was limonene, a substance used to give a citrus smell in scented candles, air fresheners and similar products.
Limonene in itself is not harmful. However, when released into the air, it reacts with the ozone to create formaldehyde.
Formaldehyde is associated with certain types of cancer, such as leukemia and nasopharyngeal cancer. The National Toxicology Program of the Department of Health and Human Services classified it in 2011 as a "known human carcinogen," according to the National Cancer Institute.
With windows and doors kept shut, formaldehyde has nowhere to go. While people enjoy the pleasant aroma of scented candles, they also unwittingly inhale the toxic formaldehyde. One way to avoid this is by opening the windows. However, in winter, this is not possible.
The researchers investigated if putting in house plants will solve the problem. They put four different kinds of house plants in the six houses and monitored the limonene and formaldehyde levels.
As the use of scented candles increased, the limonene levels rose. However, the formaldehyde levels dropped when the plants were placed inside the house, indicating that the plants absorbed the toxic substance. Some plants, including lavender, are known to be good absorbers of formaldehyde.
"Our experiment has shown that you have control over the levels of these chemicals in your home. If you want less of a chemical like limonene in the air, then use fewer fragranced products such as air fresheners and scented candles, and choose fragrance-free cleaning products where available," concluded the "Trust Me, I'm a Doctor" team.
