What is the substance in tobacco products that causes stained teeth and skin?

Nicotine and Tar are the two major components of tobacco that causes teeth staining. Just like our skin, our teeth have pores, which can easily absorb nicotine and tar and turn white teeth yellow. Although nicotine itself is colorless but when it combines with oxygen it turns yellow. Even nicotine infuses electronic cigarettes causes teeth discoloration.  

Most people have dark brown stains on their teeth, it is because of the way they consume tobacco. When tobacco is chewed along with saliva, it produces dark brown liquid which is extremely staining.

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