Final answer:
Tar is the substance in tobacco products that causes stained teeth and skin.
Step-by-step explanation:
The substance in tobacco products that causes stained teeth and skin is Tar. Tar is a sticky, brown substance that is produced when tobacco is burned. It contains chemicals that can stain teeth and skin when it comes into contact with them. This is one of the many harmful effects of tobacco use.
Learn more about Effects of tobacco use