Scientists have found some perfumed products in the home can create unhealthy levels of formaldehyde, for example scented candles. In view of its widespread use, toxicity, and volatility, formaldehyde is a significant consideration for human health.
In 2011, the US National Toxicology Program described formaldehyde as "known to be a human carcinogen".
An interesting article that talks a bit of it:
With the winter winds howling at the door, the thought of battening the hatches and lighting a scented candle is understandably appealing.
But new research suggests scented candles could actually be far more harmful than previously thought, giving off potentially dangerous levels of the toxic substance formaldehyde.
A study carried out by Professor Alastair Lewis of the National Centre for Atmospheric Science at the University of York found that an ingredient commonly used to give candles their scent mutates into formaldehyde upon contact with the air.
The ingredient in question is limonene, which is used to give citric-scented candles their aroma. In its unaltered state limonene is considered so safe that it is used to flavour food, as well to give cleaning products and air fresheners a lemony scent.
But limonene also reacts with naturally occurring ozone when released into the air, causing one in every two limonene molecules to mutate into formaldehyde.
While it is already well known that limonene, which occurs naturally in plants, can degrade into formaldehyde, almost every test into its harmful impacts was carried out decades ago.
Professor Lewis’ concerns are therefore two-fold. Firstly the concentrations of limonene he found in scented candles were up to 100 times higher than previously thought.
Secondly homes now let so little energy and air escape that these high concentrations of formaldehyde linger longer and can cause long term harm.
Speaking to the Telegraph he said: “The really surprising thing is just how high the concentrations of some fragrances are now in people’s homes…Fragrance chemicals now completely dominate the inside of most homes.”
“The issue is we don’t really know what the consequences of long-term exposure to formaldehyde are. It is a chemical that is known to harm you long-term,” he added.
Taken from Telegraph.
