The big difference is in quality. Cigarettes are adulterated with tons of chemicals and waste tobacco that has been reprocessed, rolled into sheets, sprayed with tobacco juice and god know what else then cut up and mixed in with everything else. Cigarettes are full of poisons and artificial garbage that isn't present in quality pipe tobacco. Some OTC pipe tobaccos use propylene glycol and some preservatives but are no where near being adulterated to the level that cigs are.