What Mainstream Smoke is and Why It's so Harmful

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What is Mainstream Smoke?

Mainstream smoke is the inhaled and exhaled smoke created while taking a puff on a lit cigarette. It is one of two components in secondhand smoke.  The second is sidestream smoke, which is the smoke that wafts off the end of a lit cigarette.

What's in Mainstream Smoke?

There are plenty of cancer-causing chemicals in mainstream smoke.  Some of them are:

  • PAHs (Polycyclic Aromatic Hydrocarbons)

The composition of mainstream smoke is affected by how the smoker inhales and exhales, so it will vary from person to person. The frequency of puffs, duration and volume all contribute to the chemical makeup of mainstream smoke, as well.

What's the Difference between Mainstream and Sidestream Smoke?

Sidestream smoke is more toxic than mainstream smoke for a couple of reasons that science has identified.

1) Incomplete burning. The temperature of a smoldering cigarette is approximately 400 degrees centigrade, and it's closer to 900 degrees centigrade during a puff. Toxic chemicals present in higher amounts because of incomplete burning are 2-naphthylamine, N-nitrosodimethylamine, 4-aminobiphenyl, and carbon monoxide. 

2) Particle size. Sidestream smoke contains smaller particles than mainstream smoke. These tiny toxic particles are more easily absorbed deep in the lungs and other cells in the body, where they can contribute to cancer and other smoking-related diseases like COPD and heart disease.

How Much Mainstream Smoke is in Secondhand Smoke? 

Surprisingly, the majority of cigarette smoke is sidestream smoke.  Just 15 percent of the smoke from a cigarette comes from mainstream smoke.  The rest - 85 percent - is due to sidestream smoke.

Non-smokers breathing secondhand smoke in an enclosed space are exposed to the worst of the toxins that cigarettes contain.

Passive or involuntary smoking is the name given to breathing in cigarette smoke when you're not actively smoking yourself.

The Risks to Your Health from  Mainstream Smoke

Breathing in mainstream smoke for the smoker means that they are also inhaling sidestream smoke lingering in the air. There is no way to breathe in one without the other.  So, the risks we look at are due to secondhand smoke, a combination of the two.

Secondhand smoke is linked to a number of cancers, including:

And, as mentioned above, the toxins in cigarette smoke also increase the risk of COPD and heart disease.  Heart disease is the biggest killer of smokers.

Read more:  Secondhand Smoke Facts

What You Can Do to Protect Your Family from Secondhand Smoke

While we can't control every environment we are exposed to, we do have authority over our own homes, where much of the secondhand smoke exposure for kids happens.  Make yours smoke-free, and do the same with your cars. This will help you and those you love avoid the dangers of secondhand smoke and another dangerous by-product of tobacco smoke, thirdhand smoke.

As the Surgeon General stated  in the 2006 report of the Surgeon General, The Health Consequences of Involuntary Exposure to Tobacco Smoke, 

There is no safe level of exposure to secondhand smoke.

It is toxic air and should be avoided at all costs.

Quit Smoking Sooner Rather Than Later

If you're a smoker who is thinking about quitting, follow the link below to get started and stop in at our support forum for real-time help.

Don't put it off and don't be afraid.  Nicotine addiction twists our thoughts and makes us think we can't live without cigarettes, but the opposite is true.  Once you've recovered, you'll see how much better life is without the ball and chain of addiction dragging along behind you day in and day out.



American Cancer Society. Health Risks of Secondhand Smoke. Updated November 13, 2015.

National Institutes of Health. National Center for Biotechnology Information. How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General

Government of Canada. Canadian Centre for Occupational Health and Safety. Environmental Tobacco Smoke (ETS): General Information and Health Effects Updated March 1, 2011.