However, Jang's study revealed nicotine actually stimulates division of cells. And when Cooke's associates tested nicotine in lab mice with artery disease and lung cancer, they discovered it promoted growth of new blood vessels in the mice.
Cooke says this discovery suggests that nicotine could be used to heal wounds or treat other disorders in which blood flow is impeded, such as diabetes (he's already found that the chemical helps wounds heal faster in animals). It's also being tested to help people with neurological disorders like Parkinson's disease and Tourette's syndrome.
But if it's not nicotine that causes poor circulation in smokers -- giving them dull skin and a drawn look -- what is it? Hard to say: Tobacco contains more than 4,000 chemicals.