TSNAs in Cigarettes and Cigarette Smoke: What Are They?

Tobacco Leaves Curing in Shed
Burley tobacco leaves air-curing in shed. Richard Hamilton Smith / Getty Images

Tobacco-specific nitrosamines (TSNAs) are thought to be some of the most potent carcinogens in tobacco products. They are unique to tobacco and present in smokeless tobacco, snuff, cigarettes, and electronic cigarette liquid. Most of the damage comes from cigarettes and cigarette smoke however, because there are so many smokers around the world.

What Are TSNAs and Where Do They Come From?

The IARC (International Agency for Research on Cancer) has identified 8 tobacco-specific nitrosamines in tobacco and tobacco smoke.

Two of them have been classified as Group 1 carcinogens, which means they cause cancer in people.

  • N-nitrosonornicotine (NNN)
  • 4-methyl-N-nitrosamino-1-(3-pyridyl)-1-butanone (NNK)

A metabolite of NNK, NNAL is also a strong carcinogen, and has been found in the urine of people exposed to secondhand smoke, whether they smoke or not.

From Nitrates to Nitrosamines

Green tobacco coming out of the field will contain nitrates from fertilizers used in farming, and to a lesser degree, from the earth plants were grown in. It doesn't contain TSNAs however—at least, not yet.

Nitrates in tobacco leaves are transformed into dangerous tobacco-specific nitrosamines when tobacco (and the nicotine in it) is fermented and cured. Processing can be done in a couple of ways, by air or heat, and the results will produce either high or low levels of nitrosamines.

TSNAs are present in finished tobacco products, which ultimately make their way into smokers' bodies, where they contribute to numerous forms of cancer.

How Do TSNAs Hurt Smokers?

TSNAs are strong carcinogens that are linked to several cancers.

Lung cancer has been shown to be closely linked to NNK, specifically, adenocarcinoma, which is the most common form of lung cancer.

Other cancers associated with TSNAs include:

    There is a growing concern that TSNAs may be associated with cervical cancer, because these carcinogens have been found in large quantities in the cervical mucus of women who smoke.

    TSNAs Can (and Should) Be Reduced in Tobacco Products

    Researchers know that TSNA levels in commercial cigarettes vary greatly, worldwide. The reason for this is multi-faceted. Tobacco type, agricultural conditions in tobacco farming, and how the tobacco is cured once it comes out of the field all play a role in the amount of cancer-causing nitrosamines present in finished tobacco.

    Burley tobacco (also known as White Burley tobacco) and the flue-curing method appear to produce the highest amount of TSNAs, according to researchers.

    The Family Smoking Prevention and Tobacco Control Act gives the United States Food and Drug Administration the power to regulate tobacco products. Researchers are calling for standards of manufacture that would reduce the levels of highly carcinogenic TSNAs to be put in place for commercial tobacco products.

    How Is Tobacco Cured?

    Burley tobacco is air-cured, which involves hanging tobacco leaves in a barn with good air flow. The tobacco is left to dry slowly over a period of one to two months.

    Air-curing produces a low sugar, high nicotine tobacco. Cigar and burley tobaccos are air-cured.

    Flue-cured tobacco is a process in which fresh tobacco leaves are hung on poles in an enclosed barn and cured with heat from a flue connected to an external fire box. This process cures the tobacco by heat without exposing it to smoke. In the 1960's, the fire box was replaced with a gas-fed heat source. This curing method produces tobacco that is high in sugar content and medium to high nicotine content. Most commercial cigarettes are flue-cured.

    Other tobacco-curing methods include:

    Fire-curing, where a smoldering hardwood fire is inside the barn with the tobacco.

    Fire-cured tobacco can take days or weeks depending on the tobacco and what it's being prepped for. Pipe, chew and snuff tobacco are fire-cured. Some cigarettes are also produced from fire-cured tobacco. Fire-cured tobacco is low in sugar and high in nicotine.

    Sun-curing involves exposing tobacco leaves to the sun for drying. Used in Mediterranean countries, this method produces what is known as Oriental tobacco. It is low in sugar and nicotine. Turkish cigarettes are 100 percent unblended Oriental tobacco. Cigars, pipe tobacco, snuff and chew are also made with Oriental tobacco.

    The factors that influence TSNAs in tobacco and tobacco smoke can and should be controlled to protect smokers and non-smokers exposed to cigarette smoke as much as possible.

    Other Carcinogenic Compounds in Tobacco

    In addition to TSNAs, 10 highly carcinogenic chemicals known as PAHs and aromatic amines are also thought to play a leading role in the risk of the above cancers in people. Both TSNAs and PAHs can be reduced in tobacco products.

    To date, science has revealed approximately 70 carcinogenic compounds in cigarettes and cigarette smoke, including 60 that are present in cigarette smoke and at least 16 that reside in unburned tobacco. The IARC lists 10 PAHs, 8 TSNAs and 45 other carcinogens as potential human carcinogens, and research continues.

    Tobacco Use Around the World

    Tobacco kills one in five adults around the world today, amounting to approximately 6 million lives lost annually to a cause that is within our control.

    If the current course we're on continues, that number is expected to grow to 10 million tobacco-related deaths a year by 2020, with 70 percent of the loss coming from under-developed countries with no tobacco control in place.

    Education about the hazards of tobacco use and support for people quitting are key to reversing this trend.

    A Word From Verywell

    There is no safe level of exposure to cigarette smoke. It is toxic air, and when it settles on surfaces, it creates toxins known as third-hand smoke.

    If you are still smoking and want to quit, start by considering the reasons why you should, and then use the resources below to get started with smoking cessation.

    Also, stop in at our smoking cessation support forum for tips from other ex-smokers who are going through what you are, or have been there and can offer sound advice. You can simply read or join in with discussions taking place. Either way, your determination will be bolstered.

    Quitting tobacco takes some work, but the discomforts are temporary.

    Don't fear smoking cessation. Think of it as a stepping stone to a much better life.

    Sources:

    American Association for Cancer Research. Levels of Tobacco-Specific Nitrosamines and Polycyclic Aromatic Hydrocarbons in Mainstream Smoke from Different Tobacco Varieties. December, 2008.

    American Association for Cancer Research. It's Time to Regulate Carcinogenic Tobacco-Specific Nitrosamines in Cigarette Tobacco. July, 2014.

    International Agency for Research on Cancer. Agents Classified by the IARC Monographs, Volumes 1–117.

    International Tobacco Growers Association. Tobacco Types.

    Tobacco Control. British Medical Journal. The Case of the Missing Nitrosamines: A Potentially Global Phenomenon. January 8, 2004.

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