How does your body digest a cigarette?

1950s smokers
Smoking in the 1950s was a gas -- noxious, cancer causing gas. See more drug pictures.
Yale Joel/Getty Images

Everybody knows now that smoking is bad for you. But that wasn't always the case. In the 1940s, '50s and '60s, Americans smoked with reckless abandon -- in their offices, in department stores, on elevators, planes and buses. In 1965, nearly half of all Americans smoked. The World Health Organization officially took a stance against smoking in the 1970s, and rates have dropped steadily ever since -- now down to 21 percent [source: AHA]. In today's society, it would be unthinkable for someone to light up at his or her office desk or in an elevator. Just try it and see what happens.

Cigarette manufacturers were forced to list the ingredients in cigarettes in 1998, so the public is now aware that there are more than 4,000 chemicals in each and every smoke. Here's a list of the 10 most dangerous:


  • Ammonia -- used to increase the absorption rate of nicotine. It's also used to clean your toilet, helps to treat wastewater (poop and pee) and is a key ingredient in liquid fertilizer.
  • Arsenic -- used as a pesticide on tobacco plants, it remains in the resulting cigarette. If you have a rat problem in your home, you can use arsenic to kill them.
  • Cadmium -- a metallic compound that tobacco collects from acidic soil. Is the battery in your cell phone low? Use cadmium to recharge it!
  • Formaldehyde -- a byproduct of cigarette smoke, this colorless gas is commonly used to preserve dead bodies for burial.
  • Acetone -- another byproduct from burning a cigarette. It's also found in nail polish remover and, like ammonia, is used to clean toilets.
  • Butane -- this byproduct is also used to help you light your cigarette, in the form of lighter fluid.
  • Propylene Glycol -- added to cigarettes to keep tobacco from drying out. What it really does is speed up the delivery of nicotine to the brain.
  • Turpentine -- used to flavor menthol cigarettes. This oil also can be used to thin paint and strip varnish from wood.
  • Benzene -- another byproduct from burning a cigarette. You can find benzene in pesticides and gasoline.
  • Lead and Nickel -- Yes, these are metals. Need we say more?

So how does your body digest these things? It really doesn't -- which is the problem with cigarettes.


What happens when you smoke?

Internal organs
Cigarette smoke permeates every nook and cranny of your body.
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The word digest implies something good. If you digest a thought, it means you carefully deconstruct it in your mind. This can lead to a better understanding. When you digest food, you break it down into a form your body can absorb and use as energy. The problem with cigarettes is that it's more about ingestion than digestion. Your body takes in a large amount of chemicals and carcinogens with each puff, and what doesn't leave your mouth or nose through exhalation stays there for a while. Our internal organs, blood and cells simply aren't built to process cigarette smoke.

When you smoke, the first thing that happens is a mix of gases is released around your eyes, nose and throat. This happens within the first few seconds. Your eyes may water, your nose might run and your throat will most likely become irritated. Tiny hairs called cilia work to clean your bronchial tubes and lungs of nasty foreign matter. They're the street sweepers of the body. Smoking paralyzes and can even kill the cilia so they can't sweep. If you smoke, the cilia that you don't kill wake back up and get out the brooms. When smokers wake up coughing, it's because the cilia are hard at work again. Then the first cigarette of the day paralyzes the poor little guys again, and the hacking cough ceases. It's no wonder that smokers in the early days didn't realize it was bad for them. If a cigarette stops the morning cough, it must be a good thing, right?


Deep inside the lungs, cigarette smoke damages the floating scavenger cells that work to remove foreign particles from the lungs' tiny air sacs, called alveoli. A lot of what you inhale turns to tar. This tar isn't unlike what you might use to pave a road or shingle a house. Only about 30 percent of cigarette tar is sent back into the air through exhalation -- the rest sticks to your throat and lungs like saltwater taffy. Besides being disgusting, tar kills healthy lung cells. A pack-a-day smoker ingests a full cup of tar into his or her lungs every year.

The myth of low-tar cigarettes is just that -- a myth. Cigarette manufacturers poke tiny little holes in the filter to "reduce" the amount of tar you ingest. Sounds good, right? Unfortunately, your fingers block most of these holes when you hold a cigarette, and low-tar smokers end up inhaling more deeply to achieve the nicotine hit they crave.

The chemicals in cigarette smoke are pretty much immediately absorbed into your bloodstream. From here they go straight to your heart and from there, everywhere else in your body. Your heart begins to beat faster as soon as you light up, as much as 10 to 25 beats per minute. That adds up to 36,000 extra beats per day. Smoke can also cause an irregular heartbeat, or arrhythmia. The oxygen level in your blood is reduced because the carbon monoxide produced when you smoke tricks the body into thinking that it's oxygen. (For more on this trick, read How does smoking starve your heart of oxygen?.) Problem is, your body's cells still need oxygen, so your heart goes into overtime to supply it.

If you continue to smoke regularly, your senses of taste and smell will slowly fade, thanks to the tar that coats your tongue and nasal passages. You probably won't even realize it's happening and may only notice what you've been missing when you quit. Most smokers who quit report a noticeable change in how their food tastes and smells.


What else happens when you smoke?

Crow's feet
Smoking causes wrinkles around the eyes, called crow's feet.
Hans Neleman/Getty Images

Another thing that happens when you smoke is that your blood pressure rises by about 10 to 15 percent. High blood pressure means you have an increased risk of heart attack and stroke. Smoking not only affects the pressure, but it also damages the blood itself. As we mentioned before, when you smoke, carbon monoxide (CO) is created and ingested -- so much that smokers have about 4 to 15 times the amount of CO in the body than non-smokers. Carbon monoxide also is the same stuff that comes out of your car's tailpipe. When you smoke, it stays in your bloodstream for about six hours. This harmful chemical compound does its best to rob every cell in your body of oxygen, something cells need to function. 

Most smokers know the damage they're causing to their lungs, heart, blood vessels, and senses of taste and smell. Something many smokers may overlook is the damage being done to their skin. While many of smoking's negative effects are reversible once you quit, there's no way to undo the skin damage. The blood vessels in the skin constrict when you light up, limiting the amount of oxygen the skin gets. The intrusion of CO puts further limits on the oxygen the skin needs. What does this mean? Wrinkles. "Smoker's face" is a condition long-term smokers suffer from. What does it look like? Deep, dark lines around the eyes and the corners of the mouth, for starters. The skin may also appear gray in color, and facial features may appear gaunt. Not a pretty sight. One study shows that nearly half of all smokers get smoker's face.


So besides wreaking havoc on your insides, cigarettes also ages you prematurely. If this isn't enough to inspire you to put down the pack, think about your sex life. Research conducted by Boston University's medical school has shown that when men smoke, it can lead to erection problems. Among the 1,011 men studied that had erectile dysfunction, 78 percent were smokers. The study found that the amount of blood flowing to the penis was directly proportional to the number of cigarettes smoked. Smoking also lowers sperm count and can even alter the shape of the little guys. So if you're looking to have kids, you may want to think about quitting. Women don't get a free pass in this department either. Ladies who smoke heavily show a 43 percent decline in fertility and reach menopause nearly two years earlier, decreasing their reproductive years.

So how does the body digest a cigarette? It really doesn't. There's the exhale, but that's simply because the body can't completely absorb every bit of smoke from the inhale. The harmful chemicals in cigarettes tear through every cell of your body like looters in a riot. The smoke affects the blood, skin, lungs, heart, your senses of taste and smell, and anything else it comes into contact with. Kicking the habit is a tough task, but it's one that's well worth the effort. You may not be able to reverse the effects of premature wrinkling, but you can help out the rest of your body. As soon as you stop, your body goes into fix-it mode. Your cilia wake up and start sweeping again, and your taste buds fight through the tar. Oxygen is again delivered in full supply to your heart and the rest of your body. The days turn into weeks and months and eventually years and before you know it, you may feel like you never lit up in the first place.


Lots More Information

Related HowStuffWorks Articles
More Great Links
  • "All about smoking." 2008.
  • "Clearing the Air on the Hard Facts of What Smoking Does to Your Body." 2008.
  • "Harmful Effects of Smoking." 2008.
  • "Smoking Cessation." American Heart Association. 2008.
  • "Smoking: Does it cause wrinkles?" Mayo Clinic. 2008.
  • "Tar Information Sheet." 2008.
  • "What happens when you smoke?" 2008.
  • "What's in a cigarette?" Signal One Smokebusters. 2008.