What chemical additives are put in cigars and why?

Cigar Smoke and Nicotine Content Researchers currently believe that as few as five milligrams of nicotine a day is enough to cause addiction to the drug. The average cigarette has around one milligram of nicotine in it, and cigars have much higher levels of nicotine – up to 400 milligrams in large, long cigars. This means that one cigar a day may be enough to cause addictive changes in your brain cells. Tobacco smoke contains more than 4,000 chemical compounds, including the following substances, which are also contained in household products with warning labels telling you to avoid inhaling them:

formaldehyde ammonia urethane naphthalene Other cigar smoke contents include the following substances:

carbon monoxide hydrogen cyanide arsenic nicotine benzene vinyl chloride ethylene oxide other volatile aldehydes cadmium radioactive polonium 210 Because of the long aging and fermentation process for cigar leaves, because of the larger size of cigars and because of the toxic way it burns due to cigars’ nonporous wrappers, cigar smoke has 20 times more ammonia than cigarettes and 80 to 90 times the number of highly carcinogenic, tobacco-specific nitrosamines. Cigar smoke also contains 30 times more carbon monoxide than cigarette smoke.

As to WHY they are added, I imagine, some add flavor, some are preservatives, and possibly some to make them more addictive.

http://www.quitsmokingsupport.com/cigars.htm