heavy metals in cigarette smoke Cigarettes as a source of metal toxicity: evaluating human health risks | Discover Public Health Fact: cigarettes contain rat poison.
Description
Cigarettes are placed into four categories as per the Centers for Disease Control and Prevention (CDC) in the US, which are as follows
Manufacturers deliberately add a chemical compound to give it a strong unpleasant smell

Causes and Symptoms of Nicotine Addiction The reason why quitting is so difficult is because of the nicotine in tobacco products

McCabe SE, West BT, Veliz P, Boyd CJ

If you're wondering what does smoking weed do to your lungs, the answer may include chronic respiratory irritation, reduced lung function, and possibly greater vulnerability to lung disease over time

Chronic infections: Reduced blood flow makes it harder for your mouth to fight off bacteria
