Preventing first use of tobacco by young people is most important, because once young people begin smoking they are unlikely to stop. All educators can play a positive role in prevention. The lung's capacity to exchange oxygen for carbon dioxide is impaired. That's how fire fighters die of smoke inhalation. In smoking, the damage is more gradual but still the same.
Tobacco smoke contains carbon monoxide.
That interferes with the blood's ability to transport oxygen to the body's cells. Tobacco damages the heart muscles. Any machine that has to work right 2 billion times has to be taken care of. Most are not able to. Tobacco is the most addictive substance known to humankind.