A study conducted by researchers from BBC, along with Professor Alastair Lewis from the University of York, found that the scent giving out a citrus odor in candles, body sprays, cleaning products and air fresheners could be causing cancer when diffused into the air, reported Independent on Friday.
The researchers studied the levels of "volatile organic chemicals" in the air of six similar houses and learned that the most common chemical was limonene.
Once released into the air, limonene interacts with the ozone producing the organic compound formaldehyde, a known carcinogenic substance since the 1980s. In 2011, it was officially listed as a human carcinogenic.
Formaldehyde is a strong-smelling and flammable chemical, usually used in various building and household products, such as is pressed wood products, adhesives, paper product coatings, permanent-press fabrics and a few insulation materials.
In amounts more than 0.1 ppm in the air, formaldehyde can cause several adverse effects, including burning sensations in the eyes, nose and throat, skin irritation, nausea, coughing and wheezing.
According to Tech Times on Saturday, the researchers also found that the level of formaldehyde in the series of houses was proportional with the level of limonene.
The goal of the study was not only to determine the levels of chemicals in the houses, but also to reduce these substances through practical ways, so they put in houseplants in each house for a duration of six weeks.
Lewis kept track of the measurement of limonene and formaldehyde the entire six weeks that the houseplants were present in the houses. After one month, he observed that limonene from scented candles and air freshener increased in level, attributed to closed windows and doors because of the weather.
The plants seemed to have no effect on the level of limonene, but caused a significant decrease in the level of formaldehyde. This led the study to suggest that houseplants are capable of absorbing hazardous compounds such as formaldehyde.
Laboratory tests also revealed that English Ivy is overall the best absorber of harmful chemicals. As for formaldehyde, geraniums, ferns and lavender are the plants of choice.