Sidestream and Mainstream Smoke: Definition and Effects

Sidestream smoke (SSM) is the smoke that is emitted from the burning end of a cigarette, cigar, or pipe. It contains many harmful chemicals and pollutants, including carcinogens, which are known to cause cancer.

On the other hand, mainstream smoke (MSM) is the smoke that a smoker inhales and then exhales into the surrounding environment. When the terms “environmental tobacco smoke” or “secondhand smoke” are used, they refer to both sidestream and mainstream smoke.

There has been much debate over whether sidestream smoke is more dangerous than mainstream smoke. Research found that sidestream smoke was 4 times more toxic in terms of total particulate matter, 3 times more toxic per gram of weight, and 2 to 6 times more likely to cause cancer.

One reason that sidestream smoke may be more harmful than mainstream smoke is that it contains a higher concentration of certain chemicals, such as:

  • Nicotine
  • Formaldehyde
  • Ammonia

Additionally, sidestream smoke produces smaller particles that can more easily penetrate the tissues in our bodies.

Since approximately 85% of secondhand smoke is sidestream smoke: both smokers and non-smokers nearby are exposed to similar levels of environmental tobacco smoke. Sidestream smoke also poses a danger for a longer period of time than mainstream smoke, as it can persist in the air and affect both smokers and non-smokers even after a cigarette has been put out.

Various factors can influence the quantity of sidestream smoke that an individual is subjected to, such as air temperature, moisture, ventilation, and the number of cigarettes consumed within a particular period.

Composition of Sidestream Smoke

Sidestream smoke contains thousands of chemicals, metals, and gases, nearly 70 of which are suspected of causing cancer. Some of the most toxic compounds found in it include:

  • Benzene, which can cause leukemia and lymphomas, and damage the immune system;
  • Phenol, a compound that promotes tumor growth and metastasis in lung cancer and is toxic to the cardiovascular system;
  • Styrene, which doubles the risk of acute myeloid leukemia and affects the central nervous system;
  • Hydrogen cyanide, which is most toxic when inhaled and can cause cell death and organ damage;
  • Formaldehyde, linked to nasopharyngeal carcinoma and myeloid leukemias and can paralyze the cilia in the respiratory tract;
  • Nicotine, the addictive component of tobacco that may work along with other toxins to create cancer and aid in its progression and spread;
  • Carbon monoxide, a poisonous gas that reduces oxygen supply to the body’s tissues and adversely affects the central nervous and cardiovascular systems.

The composition of sidestream smoke differs from mainstream smoke, with higher concentrations of certain chemicals due to the incomplete burning of tobacco.

Effects of SSM on the Body

Sidestream smoke:

  • Affects the autonomic nervous system, the part of the nervous system that regulates the heart and influences blood pressure;
  • Damages the large airways (the bronchi) and the smallest airways (the alveoli) of the lungs;
  • Produces a greater number of leukocytes, the white blood cells in our immune systems that respond to abnormal substances in the body and fight infections;
  • Decreases the elasticity (flexibility) of the lungs, and increases susceptibility to (and severity of) asthma and respiratory infections like the flu and the common cold;
  • Promotes atherogenesis, and the build-up of plaque in arteries which can result in conditions such as heart attacks and strokes;
  • Predisposes babies who are exposed in utero (while in the womb) to early heart disease.

Effects of Smoking on the body

More in general, smoking:

  • Damages almost every organ in your body, including the lungs, heart, blood vessels, reproductive organs, mouth, skin, eyes, and bones;
  • Causes cancer, including lung cancer, bladder cancer, and cancer of the pancreas, kidney, and cervix;
  • Causes respiratory diseases such as chronic bronchitis and emphysema, and increases the risk of developing heart disease and stroke;
  • During pregnancy, can harm the developing fetus and increase the risk of premature birth, low birth weight, and sudden infant death syndrome (SIDS);

Quitting smoking at any age can improve your health and reduce your risk of developing smoking-related diseases.

Dangers and Risks of SSM:

  • Sidestream smoke is a class A carcinogen, indicating it can cause cancer;
  • Certain groups are at greater risk, such as pregnant women, young children, and those with medical conditions;
  • Pregnant women and young children have an increased risk due to their time period of rapid cell division, and because unborn babies and children have a longer time to live with the damage caused by sidestream smoke;
  • The latency period, which is the time between exposure to a carcinogen and the development of cancer, is of greater concern for younger people than older ones;
  • People with heart and lung-related conditions such as asthma, COPD, lung cancer, and coronary artery disease are at an increased risk of harm;
  • Exposure to secondhand smoke increases the risk of lung cancer;
  • Sidestream smoke may also increase the risk of breast cancer, and exposure to it is just as important as active smoking when it comes to the risk of breast cancer.

Sidestream smoke is a major cause of concern; the toxic particles it produces settle on surfaces and linger for an extended period of time. Even after sidestream smoke has visually disappeared and dissipated into the environment, it still poses a risk. Researchers are now concerned about the dangers of what they call “thirdhand smoke”.

The toxic particles present in sidestream smoke settle as particles in the area where someone has been smoking and remain on surfaces for a long time. These toxic particles include arsenic and cyanide, among others.

Thirdhand smoke can pose a problem in a few ways:

  • These toxins may be absorbed through the skin, especially in toddlers who crawl around;
  • The particles may be released back into the air as gases in a process called off-gassing.

In summary, both sidestream smoke and mainstream smoke have harmful effects on your health. The main difference between them is that sidestream smoke comes from the burning end of a cigarette, while mainstream smoke is exhaled by the smoker.

It’s important to note that smoke exposure doesn’t stop when a person puts out their cigarette. Smoke particles can linger in the air and affect the health of those around them over time. This can increase the risk of developing cancer and heart disease.


Humanitas is a highly specialized Hospital, Research and Teaching Center. Built around centers for the prevention and treatment of cancer, cardiovascular, neurological and orthopedic disease – together with an Ophthalmic Center and a Fertility Center – Humanitas also operates a highly specialised Emergency Department.