Student Guest Post: Arsenic, Benzene, and Now Clostridium? Smokers are Inhaling More Than Just Chemicals in Their Cigarettes

It's time for this year's second installment of student guest posts for my class on infectious causes of chronic disease. Second one this round is by Jonathan Yuska. 

If you happen to be one of the 46 million individuals who have not been swayed to quit smoking by the countless anti-cigarette ads in print and on television, here is one more piece of evidence that may have you second thinking that next puff. On top of the more than 3,000 chemicals and heavy metals already identified in ordinary cigarettes1, upwards of a million microorganisms per cigarette have also been found to live and thrive in virtually all cigarettes in the United States2. Microbes such as Bacillus (which is linked to the notorious anthrax disease), Clostridium, and Pseudomonas—to name a few—likely contaminate the tobacco leaves early at the farm level and are able to flourish during curing and manufacturing to be viable in the cigarette at the time of the consumer’s use. While some of the bacteria are capable of causing no more than a stomachache, others (and their respective endotoxins) have been linked to pneumonia and chronic lung inflammation—a widely recognized risk factor for cancer1,2. While cigarette smoking is a well-established cause of cancer in and of itself, the role microorganisms have in the toxicity of cigarette smoke should not go underplayed. With increasing evidence supporting the vast illness causing biodiversity found in cigarettes, hopefully more individuals will be aware of the dangerous contaminants they are welcoming into their bodies and call for greater sanitary measures to be taken to potentially create a less harmful cigarette product.

Approximately 23 different species of bacteria have been found in cigarette tobacco, many of which have been linked to serious illness in humans. For example, Pseudomonas aeruginosawhich is the leading cause of nosocomial pneumonia and often found in soil or sand—was found to be present in nearly all cigarettes tested in a study that looked at the presence of cigarette bacteria in the most commonly smoked brands, like Marlboro2. Another study interested in understanding the cause of severe lung inflammation in United States troops during Operation Iraqi Freedom found eight different species of Bacillus (five of which were never seen before) contaminating the soldier’s cigarettes3. Regardless of the actual bacteria within the cigarettes, the endotoxins derived from the bacteria that remain well after the bacteria have died have been shown to be a powerful inducer of lung inflammation (chronic inflammation is recognized as a powerful risk factor for cancer). It is theorized that the bacteria and their respective endotoxins may have an additive or multiplicative effect with tobacco smoke’s natural ability to cause pulmonary inflammation, though the amount of the effect that can be attributed is still up to debate2.

Research has shown that more than 90 percent of cigarettes are contaminated with some form of bacteria, and these bacteria are believed to originate early in the cigarette manufacturing process1. Similar to other crop cultivation, tobacco is grown in large fields where animal manure is used to provide the nutrients needed for a hearty crop. Some of the bacteria from the manure are believed to adhere to the tobacco leaves during the plant’s development. Curing the tobacco, which is essential in the cigarette manufacturing process to develop an ignitable, flavorful product, further facilitates bacterial growth because it is often done in moist, warm conditions3. Unlike other agriculture crops grown for consumption, tobacco has no regulations associated with its sanitation, and as a result, tobacco products can contain soil residues and insecticides in addition to a vast array of deleterious bacteria. Efforts to sanitize tobacco through an antimicrobial wash have been proven to be effective in reducing contaminants; however, since so little mainstream attention has been given to microbes in cigarettes, no sanitation process is currently being used by the cigarette industry2.

Misperceptions about how much risk the bacteria pose to the smoker is one reason so little attention has been given to microbes in cigarettes.  Some critics believe that bacteria in cigarettes pose no harm because the cigarette flakes are prevented from entering the lungs because of the built-in filter within the cigarette. Some further argue that the viable bacteria found in the tobacco are destroyed or heavily reduced in number by the heat of the cigarette. Though, the validity of these observations are derailed by the fact in the process of transportation, or even minor jostling, tobacco flakes are often seen lying freely on the mouth end of the filter. Thus, loose tobacco on filters could transfer bacteria to the mouths and lungs of smokers before the cigarette is even lit. Additionally, some extremely fine tobacco microparticulates are able to pass through the cigarette filters currently being used and can be inhaled deep into the lungs to cause inflammation2,5. The harsh, high temperature conditions of cigarette smoking also does little in eliminating the bacteria that are able to produce robust heat resistant endospores such as the bacterial species Bacillus and Clostridium1. It is clear that more attention should be given to dismiss the misperceptions of bacterial risk associated with cigarettes so that effective sanitary regulations can be applied to tobacco similar to other widely consumed foodstuffs.

If the more than 3,000 chemicals and heavy metals that have been identified in ordinary cigarettes have not influenced you to quit smoking, hopefully the realization that one cigarette can contain roughly 1,000,000 microorganisms will have you second thinking the habit the next time you light up. Microorganisms that have been linked to serious illness in humans like pneumonia and chronic inflammation are thought to contaminate tobacco leaves early in the manufacturing process, and these organisms thrive and multiply to be viable bacteria in the consumer cigarette. While cigarettes themselves are recognized as a serious cause of ill health, the role microorganisms have in their toxicity should not be underplayed. With a better understanding of the vast bacterial biodiversity within cigarettes, sanitary regulations that eliminate bacterial contamination should be mandated to potentially make a less harmful tobacco product. Though until then, people should recognize the dangerous bacterial contaminants they are welcoming into their bodies every time they light up.


1.   Sapkota, Amy R., Sibel Berger, and Timothy M. Vogel. "Human Pathogens

Abundant in the Bacterial Metagenome of Cigarettes." National Center for Biotechnology Information. 22 Oct. 2009. U.S. National Library of Medicine. 13 Apr. 2013 <;.

2.  Pauly, J. L., J. D. Waight, and G. M. Paszkiewicz. "Tobacco flakes on cigarette filters

grow bacteria: A potential health risk to the smoker?" Tobacco Control. 18 Oct. 2007. 13 Apr. 2013 <;.

3. Rooney, Alejandro P., James L. Swezey, Donald T. Wicklow, and Matthew J. McAtee.

"Bacterial Species Diversity in Cigarettes Linked to an Investigation of Severe Pneumonitis in U.S. Military Personnel Deployed in Operation Iraqi Freedom." Current Microbiology 51 (2005): 46-52.

4. "How to Grow Tobacco." How To Grow Stuff. 23 Nov. 2007. 13 Apr. 2013


5. Pauly, John L., and Geraldine Paszkiewicz. "Cigarette Smoke, Bacteria, Mold,

Microbial Toxins, and Chronic Lung Inflammation." National Center for Biotechnology Information. 09 July 2011. U.S. National Library of Medicine. 13 Apr. 2013 <;.



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