A candle is a candle right? Well not really. The cheap Paraffin based ones that a readily available almost anywhere will with continued and regular exposure increase the amount of this petroleum product. These and many 'scented' candles are often laced with chemicals, often carcinogenic which when lit do you and your health no good whatsoever and are in fact detrimental to it.
The candles I recommend are Beeswax candles. They help to purify and ionise the air, which drags contaminants in it to the ground where you can with regular cleaning then remove them from your environment. They are brighter than normal candles and burn longer too. Which in a lights out situation is useful. The white residue that builds up on them can also be used on the skin.