One of the better abbreviated explanations I've seen is from one of our soy candle suppliers, Eco Candle Company.

See complete article at www.ecocandle.com/benefits

paraffin wax is used in more than 95% of candle making done today, mainly because it is very inexpensive. paraffin is the leftover by-product from the petroleum refining process. studies have shown that this petroleum by-product can release the same harmful carcinogens into the atmosphere as your car produces when gasoline is burned. when a paraffin candle in burned, it produces toxic petrol-carbon soot, which can blacken walls, furniture and ceilings and contaminate venhilation ductwork in your home. this soot goes into the air you breathe and can be hazardous to your health.  in 1986, proposition 65 was passed with the intent to protect california citizens and the state's drinking water sources from chemicals known to cause cancer, birth defects or other reproductive harm, and to inform citizens about exposures to such chemicals.  paraffin candles contain up to 11 of these known carcinogenic compounds.  these 11 compounds have been deemed 'toxic air contaminants' by the state of california. this is not only a health problem, but it is also a moral problem. we need to demand safer alternatives.