So let's begin with number one smoking, perhaps the most common one. So why is smoking bad for us? Why are cigarettes bad for us? Well, the cigarette butt contains many different types of carcinogens and a carcinogen is a cancer causing agent. So it's a molecule that when reacts with molecules in the cells of our body, can basically lead to cancer and cancer cells. So when that individual smokes, they inhale all those different carcinogens and those carcinogens eventually end up in the blood of that individual.