There is this theory (and if it wasn't, it is now) that, beside nicotine, there are three main factors that attribute to the danger of tobacco smoke, be it primary or secondary...

  1. Pesticides and herbicides used when growing the tobacco plants are still contained in the tobacco when you light up your cigarettes, cigars or whatever.
  2. Most commercial tobacco products contain sugar. Usually added by mixing the tobacco with molasses (don't ask me for details). Cigarettes contain about 5% sugar, cigars 20%, pipe tobacco has the lead with about 40% molasse/sugar. (numbers from a report by Medical World News (1973)).
  3. Most commercial tobacco products contain perfumes.

A lot of the harm done by tobacco smoke can probably be attributed to those additives. A German magazine (├ľko-Test) did a test of tobacco products in the 90's and found scary amounts of herbicides and pesticides. Back in 1972, the BBC reported that the sugar is one of the main reasons for lung cancer, they based this statement on statistics showing that lung cancer is less frequent in areas where tobacco products contain less sugar. Quote:

The late Dr. Richard D. Passey of London's Chester Beatty Research Institute had spent twenty years investigating smoking and cancer. 'In Russia, China, Formosa, and other countries where cigarettes are made of air-dried tobacco (three months in a barn, allowing fermentation of sugars, and thus resulting in no sugar content) - close to the kind the American Indian used before the invention of sugar sauces (usually with many additives) - they are unable to find any correlation at all between smoking and lung cancer.' (Sugar Blues, 1975)

I am not an expert in any of the areas concerned, I'm merely a nicotine addict, so please take this info with a grain of salt.