Some people claim that some emit harmful substances when they burn. In order to put this claim to the test, you should understand how a candle works. In a candle, it is the wax that does most of the burning. Wick, on the other hand, just disintegrated due to the heat. So, if any harmful fumes come from them, they should come from the wax. Among the three types of waxes that are used in candles, beeswax and soy wax are completely safe. Then there are the paraffin wax products. In fact, there is one study that suggests that paraffin ones emit toluene when they burn. But others claim that this study itself is questionable.