Paraffin candles comes from crude oil during the production of lubricating oils. It produces carcinogens and soot when burned. In fact, one air quality researcher stated that the soot from a paraffin candle contains many of the same toxins produced by burning diesel fuel.
Soy candles is derived from the processing of soybean oil. Micheal Richard, the inventor of soy wax, tested different natural plant waxes and finally ended up with a vegetable wax which was made with partially hydrogenated soy oil, coconut oil and palm oil. He also blended beeswax with soy wax to make an economical natural soy wax candle.
The obvious answer to why soy candles are better than paraffin candles is that one product is derived from sustainable resources (soy), whereas the other is derived from limited resources (fossil fuels).
It is a myth that soy candles do not produce any soot, although as a rule, that soot is not the black soot we find with paraffin wax candles. Whenever you have combustion of any type (the burning of a fuel), you get a certain amount of by-product carbon, whether it is detected by the human eye or not. However, the simple carbon exposure to soy candle soot is the equivalent to the exposure you would have to something cooking on your stove in cooking oil. Negligible.
Why use soy wax in candles? Again, the answer is simple. Soy is a natural, sustainable resource, limited only by the amount of vegetable matter we can produce. Soy candles are also a favorite of environmentally conscious consumers. Made from American-grown soybeans, it's a biodegradable, renewable resource.