An international study has found cigarettes are "widely contaminated" with bacteria, including some which can cause diseases.
A University of Maryland environmental health researcher and microbial ecologists at the Ecole Centrale de Lyon in France conducted the research.
The study found "cigarettes themselves could be the direct source of exposure to a wide array of potentially pathogenic microbes among smokers and other people exposed to secondhand smoke."
Lead researcher Amy R. Sapkota, an assistant professor in the University of Maryland's School of Public Health, said: "We were quite surprised to identify such a wide variety of human bacterial pathogens in these products.
"The commercially-available cigarettes that we tested were chock full of bacteria, as we had hypothesized, but we didn't think we'd find so many that are infectious in humans.
"If these organisms can survive the smoking process - and we believe they can - then they could possibly go on to contribute to both infectious and chronic illnesses in both smokers and individuals who are exposed to environmental tobacco smoke."
The study found a broad array of bacterial diversity, ranging from soil microorganisms to potential human pathogens, in commercially available cigarettes.
The study hinted that numbers of microorganisms in a cigarette may be as "vast as the number of chemical constituents."
Sapkota concluded: "Now that we've shown that a pack of cigarettes is loaded with bacteria, we will conduct follow-up research to determine the possible roles of these organisms in tobacco-related diseases."