Smoking cigarettes dramatically increases a person's risk for a host of diseases. The nicotines is addiction but it's the hundred other chemicals in cigarette smoke that are toxic. 

Because e-cigarettes are simply diluted nicotine vapor, no cigarette smoke, they should be less harmful. The U.S. Food and Drug Administration (FDA) classifies many liquid flavorings in e-cigarettes as "Generally Recognized as Safe," for oral consumption. Though it sounds like waffling, that is the default categorization. 

But because nicotine vapor still goes into the lungs, a different mechanism than nicotine patches or gums, it is unclear how safe they are over the long term. 

Ilona Jaspers, PhD, professor of pediatrics and director of the curriculum in toxicology at the University of North Carolina School of Medicine, recently completed research showing how the chemicals in e-cigarettes can change immune responses in our airways. 

"The digestive systems and respiratory systems are very different," said Jaspers, the deputy director of the UNC Center for Environmental Medicine, Asthma and Lung Biology. "Our stomachs are full of acids and enzymes that break down food and deal with chemicals; this environment is very different than our respiratory systems. We simply don't know what effects, if any, e-cigarettes have on our lungs."

It is known that cigarette smoking  impairs the immune responses of mucosal cells within the respiratory system and since e-cigarettes have risen in popularity, they are getting closer scrutiny. 

The team obtained tissue samples of the epithelial layer inside the nasal cavities of smokers, non-smokers, and users of e-cigarettes. The researchers then analyzed changes in the expressions of almost 600 genes involved in the function of the immune responses. They also obtained nasal lavage fluid, urine, and blood samples from participants to study the changes in genetic and proteomic markers of tobacco and nicotine exposure, as well as other markers of inflammation or immune responses. 

Data show that smoking cigarettes causes suppression of several key immune genes in the nasal mucosa. E-cigarette users showed the same changes in those genes, and they also demonstrated suppression of several additional immune genes, suggesting an even broader effect on the respiratory mucosal immune response system.

Certain effects of e-cigarettes might depend on the flavoring. In separate experiments using cell cultures, they examined the effects of cinnamon-flavored e-liquids and cinnamaldehyde - the chemical that makes an e-cigarette taste like cinnamon. 

"We found that cinnamaldehyde e-liquids have a significant negative effect on epithelial cell physiology," Jaspers said. "The chemicals compromise the immune function of key respiratory immune cells, such as macrophages, natural killer cells, and neutrophils."

The compromised immune function of the respiratory immune cells could signal the first in a cascade of cellular mechanisms that lead to impaired immune responses in the lung.