Why don't cigarette companies list their ingredients?

According to the CDC (Center of Disease Control & Prevention), current regulations require tobacco companies only to disclose levels of tar and nicotine on cigarette cartons. It would take a very large carton, however, to completely list the 600 odd additives contained in a single cigarette. Some of these include butane, formaldehyde, arsenic,ammonia, methane, and acetone.

From: Anitha @ Fidelity ( Bangalore )