"We realize that during this time of the year candles are very popular as gifts, and they play an important role in holiday traditions and ceremonies," Hammer said. "But, because it's winter, people commonly have their houses closed up, so there is little ventilation inside and soot levels from these candles can become dangerously high."

Soot is produced from the incomplete combustion of carbon-containing fuels. Complete combustion, identified by a blue flame as seen with gas stoves, does not generate soot, whereas yellow flames, such as those emitted by candles, typically indicate soot production.

Although candles may seem harmless, some varieties can produce indoor concentrations of soot that exceed levels allowed in outdoor air by the U.S. Environmental Protection Agency.

"Soot particles are very small - less than 1 micron - and easily penetrate to the deepest areas of the lung and, according to research, can stay in the lungs for a considerable period of time," Hammer said.

Studies have shown that microscopic soot particles can aggravate respiratory illnesses. Although researchers have studied the health risks of soot from diesel exhaust and factory emissions, no studies have focused specifically on residential exposure to candles.

Hammer said candle-produced soot particles can penetrate almost all residential air conditioning filters, circulating the particles throughout the home.

In addition to possibly causing health problems, soot can deposit on surfaces in the home causing what has been called "ghosting" or "carbon tracking." Soot tends to accumulate in cool areas, often forming dark areas on baseboards, around air conditioning vents, in or near refrigerators and on wall surfaces over studs. It also is attracted to electrically charged surfaces, including certain plastics and computer screens.

"Sometimes we confuse these dark areas for mildew or mold, and we find these areas are very difficult to clean, almost impossible, because they are oily," Hammer said. "People don't anticipate this to be soot when it actually is."

For the candle enthusiast, she offers the following tips:

* Check for hard wax - avoid soft or gel candles.

* Unscented candles produce less soot than their aromatic counterparts.

* Thin, braided wicks that curl when burned are ideal - steer clear of thick or wire-core wicks.

* Candles should have a low, even flame when burned.

* Tapered and votive candles tend to burn cleanest -- avoid candles that have been poured into glass jars or ceramic containers.

* Check multi-wick pillar candles periodically to ensure even burning.

* Many candles come with instructions - take a moment to look them over since some candles require special maintenance.

Hammer also suggested keeping lit candles away from drafts created by open windows, fans or air conditioning vents -- candles in a draft could produce up to 50 percent more soot. If people burn multiple candles over the holidays, they should periodically ventilate their home by opening windows.

"This is a busy time of year for the use of candles," Hammer said. "It's a time where people need to be aware of the potential health and home care implications that go along with it. "

Note: If no author is given, the source is cited instead.

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