Cigarette stains are caused by the tar and nicotine in cigarettes. These substances adhere to your skin and create a yellowish-brown stain. The severity of the stain will depend on how much tar and nicotine is in the cigarette, how often you smoke, and how long you've been smoking.
Removing stains from your fingers can be difficult because the skin on your hands is constantly exposed to dirt and other substances that can cause staining.