Hi, I'm not sure of the exact percentage, but I can tell you that smoking greatly increases your risk of lung cancer. I had to watch my late dear mom die from lung cancer and needless to say, it was a very hard to hear Mom cry and all but pray to die she was in so much pain. I was with her most of the nights the last six months of her life and when I see people smoking ( especially the youth of today ), it brings back very painful memories of how much my dear Mom suffered. Outside of her smoking, that was the only known vice that I know of she did; like so many others, she had peer pressure influence her at age 13 and smoked ( although much less the last ten years )until she died at age 71. Mom wanted me to tell as many people as I could the dangers of smoking and I've vowed to follow her last requests, especially warning people of the dangers of smoking. I have good friends that smoke, and I respect they're decision to do so, but they all know I'm not going to be in an enclosed space ( room or car ) with them smoking and they're respectful enough to not expose me to they're second hand smoke. I will only patronize a restaurant if its totally smoke free--not those who have a separate area for smoking, for the smoke is still obvious and I'm not going to knowingly subject myself, family or others to the foul odor and proven cancer causing substances within second hand smoke. When you really stop and think about it, it makes no sense to smoke to begin with; plus, its an expensive habit that is only getting more costly and that money one would spend on tobacco, they could spend on something healthy or just save the money all together. Watching Mom die such a horribly painful death from lung cancer and emphysema was something I'd never forget; please, if you smoke, quit for your sake and the ones who love you. God bless, Mark Savage/Inspectorgadget1956