Use clean-burning beeswax, and keep the wick clipped to keep chemicals and soot from hindering indoor air quality.

Beware: Too many candles could be gravely unhealthy.

RODALE NEWS, EMMAUS, PA—Candles help you set the mood or just relax at the end of the day. However, they can also add nasty pollutants to your indoor air, according to a study presented at the recent meeting of the American Chemical Society.

THE DETAILS: Most of the candles on the market are made with paraffin wax, derived from petroleum, and scented with synthetic fragrances, also derived from petroleum. Less common are candles made from plant oils like soybean, palm, or hemp, or from beeswax. The researchers for this study took paraffin wax and soy wax candles and burned them for five to six hours inside a chamber, measuring the kinds of chemicals that could be emitted by burning candles. They found varying levels of cancer-causing toluene and benzene, as well as other hydrocarbon chemicals called alkanes and alkenes, which are components of gasoline and can irritate respiratory tracts and trigger asthma. Ruhullah Massoudi, PhD, professor of chemistry at South Carolina State University and lead author of this new study, says that his research didn't reveal the exact amounts of the pollutants he found, only that they were there.

WHAT IT MEANS: Chemicals that reduce your indoor air quality aren't the only problem with paraffin candles. Previous research into candle pollution has found that candles can emit ultrafine, lung-damaging particulate matter that's capable of penetrating deep into the lungs. Massoudi adds that candle soot can deposit on furniture, in carpeting, and in walls, lingering for long periods of time. A study from the Canadian Mortgage and Housing Authority found that candles can contribute to everything from stains on carpet to black dust on household surfaces and blackened, greasy air filters.

The amount of soot and chemicals produced by a single candle can be hard to predict, as well. An Environmental Protection Agency report on candles and indoor air quality found that one type of candle could emit 100 times more soot than another. While burning a single paraffin-wax taper or tea light now and then probably won't pollute your home, frequent candle users may want to look for alternatives to keep their indoor air quality as healthy as possible.