As you take the first drag, smoke passes through your mouth, leaving a faint brown film on your pearly whites. Toxic gases such as formaldehyde and ammonia immediately put your immune system on alert, causing allover inflammation.
Once in the windpipe, the cigarette smoke temporarily slows your cilia, the tiny sweepers that work to clear your respiratory system of mucus and invading particles. Meanwhile, airborne nicotine passes instantly into your bloodstream through the millions of capillaries in your lungs.
Your body gets a jolt of energy as that nicotine hits your adrenal glands, triggering an outpouring of adrenaline that raises your blood pressure and heart rate. Your heart is unable to relax fully between beats—and you are now at a higher risk of having a stroke.
At the same time, carbon monoxide (a toxic component also found in car exhaust) from the smoke is starting to build up in your blood, limiting your body's ability to transport oxygen to your vital organs.
Via the blood-stream, nicotine hits your brain, where certain nerve cells respond by letting loose a torrent of the feel-good neurotransmitter dopamine.
After 5 Minutes
As dopamine levels quickly plummet back to normal, your body yearns for another high—even if you're not aware of it. If you frequently give in to the craving, your brain will get hooked and you'll crash into withdrawal when you try to stop smoking (some experts posit that nicotine could be just as addictive as heroin).
The cigarette smoke is gone, but your body will be mopping up toxic substances for the next six to eight hours.