Wish I could downvote this bullshit. It cites a 2009 study that merely produces small amounts of toxic chemicals. Here's a 2014 study that says this: "Potential consumer health risks associated with the candle emissions were characterized by comparing the exposure concentrations with existing indoor or ambient air quality guidelines or, where not existent, to established toxicity thresholds. On the basis of this investigation it was concluded that under normal conditions of use scented candles do not pose known health risks to the consumer."
Incomplete combustion produces smoke containing pollutants that cause disease.