The nicotine and tar in smoke will stain your teeth, it will cause and accelerate gum disease which may lead to tooth loss, you may get bad breath and it also increases your risk of developing mouth and throat (and obviously lung) cancers. Smoking reduces the blood and oxygen supply to the gums. Quite often this will mean that if you smoke your gums don’t bleed (first warning sign of gum disease), even though they are very unhealthy.