Tobacco is not technically a drug, but the nicotine within is the addictive drug like agent. Tobacco smoke however is highly toxic, and produces several thousand chemicals including hundreds of toxic chemicals such as Formaldehyde, Hydrogen Cyanide, cyanide, and hundreds of other chemicals. It can be easy to see why damage to direct contact to smoke can happen. Additionally damage to the lungs decreases the ability to absorb oxygen resulting in skin discoloration. Smoke also has mutagen effects which can make cancer a very real possibility.