Burning candles made from paraffin wax the most common kind used to infuse rooms with romantic ambience, warmth, light, and fragrance is an unrecognized source of exposure to indoor air pollution, including the known human carcinogens, scientists report.

Levels can build up in closed rooms, but ventilation can reduce them, they indicated in a study presented at the 238th National Meeting of the American Chemical Society.

Candles made from beeswax or soy, although more expensive, apparently are healthier, said researchers R. Massoudi and Amid Hamidi. They do not release potentially harmful amounts of indoor air pollutants while retaining all of the warmth, ambiance, and fragrance of paraffin candles, which are made from petroleum.

“An occasional paraffin candle and its emissions will not likely affect you,” Hamidi said. “But lighting many paraffin candles every day for years or lighting them frequently in an unventilated bathroom around a tub, for example, may cause problems.”

Besides the more serious risks, he also suggested that some people who believe they have an indoor allergy or respiratory irritation actually may be reacting to air pollutants from burning candles.