system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do cigarettes contain so much harmful stuff? Why not just tobacco?
gpt
Much of that harmful stuff it the tobacco / what happens if you burn anything. 

Some of it is added for for the benefit of the user like menthol to relax the throat and aid in nicotine absorption.  And chemicals to aid in holding an ember so you don't have to keep relighting your cigarettes.