Tobacco smoking wreaks havoc on the endocrine system. The poisons we ingest from tobacco smoke has a well-documented suppression effect on our hormone production. For those who suffer from low testosterone, this is basic, the first thing that has to be done before treatment is to quit smoking.
When you suddenly quit smoking tobacco after years of subduing your body's natural chemistry with poisons, chemistry that your body has long compensated for as best it can, the endocrine system is released from it's bondage. Your body has to readjust to the sudden increase in hormone levels. Essentially, to a degree, you get to go through puberty all over again. YAY!
Like the pre-teen years, you get acne all over again, your libido will increase with the effects that accompany that (the inability to roll over in the AM due to the reinstallation of the kickstand was the most notable to me), and other more subtle changes. Fortunately, this time around you don't have the peer pressure like before, nor the worry about who you'll go to prom with.