Bad News If You Like Scented Candles

If you're a lover of scented candles, we have bad news. One of their most common perfume ingredients, limonene, may turn into carcinogens when it's floated into the air of our homes. A new study this month for the BBC by a team at the University of York highlighted what many people don't seem to realize about putting cozy candles around their home: the level of limonene, a citrus extract used in a lot of tasty-smelling candles, has a nasty tendency to turn into formaldehyde. Yes, that's the chemical they use to preserve medical specimens that can lead to respiratory problems and various types of cancer.

I'm not much of a scented candle girl, but it's fairly common to want the delightful waft of something fresh in the house, particularly in winter months, or when the cat has done something vaguely disgusting. If you're a massive fan, though, it pays to be aware of the chemical price you may be paying, and how to minimize possible damage being done by candle over-use.

So here's the real story about why scented candle chemicals should cause concern, and how you might be able to fight the side effects — and keep your lavender candles too.

The Dangerous Thing About Scented Candles

The York study outlined the basic process in which specific gorgeous candle scents turn into nasties. Limonene, the citrus extract that's used in a lot of air fresheners and candles because of its delightful scent, has an interesting chemical reaction when it's released into the air. Once it comes into contact with ozone, some of it transforms into formaldehyde in the air.

Granted, the study was tiny: it only analyzed the air quality in six houses. But the results were interesting anyway. The more limonene in the air of a house (usually because they burned lots of candles and used air fresheners), the more formaldehyde was hanging around too. If there's no limonene, you seem to face no formaldehyde risk whatsoever (though, as we'll discuss later, burning anything inside the house has its own risks).

Why Formaldehyde Is A Problem

Formaldehyde isn't just for preserving dead things in big jars. Even though that's what it's most famous for, it's actually found nowadays as a particulate, hanging around in the air. It's sometimes used in furniture, insulation, and in certain cleaning products, and has been the target of a lot of studies about its potential health effects. (It's also sometimes found in hair-straightening products, so watch out for that as well.)

Short-term exposure to high levels of formaldehyde seems to be associated with respiratory disorders, asthma, irritation of the nose, throat and eyes, and erosion of the gastrointestinal tract. Longer-term exposure, which is what we're talking about here, is also an issue. The National Cancer Institute classifies formaldehyde as a "probable human carcinogen," meaning that it raises the likelihood of developing cancer, specifically myeloid leukemia. (This is why a 2012 study that found many Californian daycares had above-legal levels of formaldehyde in their air caused such a furor.)

Are Incense Any Better?

Sorry, but we've known that incense might be a problem for even longer. A 2009 study of formaldehyde levels in indoor incense burning found that incense cones and sticks release large amounts of formaldehyde into the air; one look at temples in China in 2002 found that the level of formaldehyde and other carbonyls (compounds of oxygen and carbon) inside temples were between 11 and 23 times the amount in the air outside. Looks like they're even worse.

So, Should You Stop Burning Candles & Incense?

If all you have to live for in the winter is your pine candle, it's important not to panic. The elevated levels of formaldehyde from candles are less than habitual incense-burning (open a window when you do that), and scientists are still defining the full extent of its health risks. It's also part of a spectrum of health warnings about burning things of any kind inside: indoor wood fires, for example, come in for criticism if they're not done properly, as they can expose everybody to fine particle pollution and its respiratory health risks. And candles of any kind are linked to lowering air quality indoors.

It does seem pretty concrete, though, that the limonene in certain scented candles may be irritating your airways and making things worse, so if you want to continue burning candles, at least look for some without that perfume.

How To Minimize Potential Candle Damage

Besides looking for candles without limonene, you might want to get some house plants. The York scientists conducted another experiment alongside the limonene-formaldehyde one. They put house plants in the candle-burning houses, and discovered something interesting: while levels of limonene didn't go down, levels of formaldehyde did.

The specific types of plants seem to have mattered. The researchers chose spider plants, dragon tree, golden pothos, and English ivy, all of which have a scientific track record of improving indoor air quality. LiveScience has a more comprehensive list of all the most effective plants for cleaning volatile compounds like formaldehyde out of your air, including peace lilies, purple waffle plants, and aloe vera.

Another important strategy has to be pointed out: opening your windows. While it doesn't seem like a particularly good idea during winter, brief ventilation likely helps a great deal for dispelling formaldehyde, even though studies haven't given us definitive numbers about it. The legal U.S. limit for formaldehyde in the air over an eight-hour day is 0.75 parts per million, and 0.1 to zero is the best. Nobody is suggesting outright banning candles, but it's incredibly important that you keep your house ventilated and have formaldehyde-sucking plants if you love to light scented ones.

So if you really can't live without your candle while you meditate, look for some without limonene, get yourself some NASA-approved plants to soak the air, and crack a window afterwards.

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