The wax used in most common candles is a source of indoor air pollution that includes known human carcinogens, researchers said at a recent health conference.

Researchers R. Massoudi and Amid Hamidi, from the University of South Carolina, said in a statement released at the National Meeting of the American Chemical Society Tuesday, that levels of pollutants from paraffin wax can build up in closed rooms and eventually become dangerous.

The researchers said that occasionally lighting the candles would likely have little health impacts, but everyday use could cause problems.

They also said that many people who think they have indoor allergies and respiratory irritation may actually be reacting to air pollutants from paraffin wax candles.