No butts about it: Smoking leads to teeth stains.

To Keep Teeth White, Don't Light Up

Not only is it bad for your health, smoking is one of the worst offenders when it comes to teeth stains. Nicotine causes brown stains that penetrate the groves and pits of tooth enamel and can be hard to remove by brushing alone. The longer you smoke, the more entrenched the stains become. Smoking also causes bad breath and gingivitis (gum disease), and increases risk of oral cancers.