Let's talk again about the dangers of smoking, because even one drag off a cigarette does a lot more damage to you than you might think. For example: With the first puff, smoke passes through your mouth and leaves a thin brown film on your teeth. Toxic gases - like ammonia and formaldehyde - throw your immune system into a panic, causing inflammation all over your body. Then, as cigarette smoke gets into your windpipe, it temporarily slows your cilia - the tiny sweeper-hairs that work to clear your respiratory system of mucus and invasive particles. With the first puff of a cigarette, you also inhale nicotine - which immediately gets into your bloodstream through millions of tiny capillaries in your lungs. As that nicotine reaches your adrenal glands, your body gets a jolt of energy that raises your blood pressure and heart rate. Since your heart can't fully relax between beats, you've just put yourself at higher risk for having a stroke. Another negative: Carbon monoxide - the toxic chemical in car exhaust - starts to build up in your blood. That makes it harder for your body to carry oxygen to your vital organs. At the same time, blood transports the nicotine to your brain - where nerve cells release a wave of the feel-good hormone dopamine. heroin - even if you have just one smoke.