A recent study by Yale researchers explains why smokers have amplified reactions to the flu virus compared to nonsmokers. The recent study also pinpointed how viruses and cigarette smoke interact to increase lung inflammation and damage.

The results of the study show that the previous hypothesis (cigarette smoke decreases antiviral responses) is false. In fact, the study found the exact opposite is true. Results show that the immune system of mice exposed to cigarette smoke from as little as two cigarettes a day for 2 weeks overreacted when they were also exposed to a mimic of the flu virus. The immune systems of the mice got rid of the virus normally; however, exaggerated inflammation caused increased levels of tissue damage.

“The antiviral responses in the cigarette-smoke exposed mice were not only not defective, but were hyperactive,” says Jack A. Elias MD, lead author of the study and chair of internal medicine at Yale School of Medicine. “These findings suggest that smokers do not get in trouble because they can’t clear or fight off the virus; they get in trouble because they overreact to it.”

“It’s like smokers are using the equivalent of a sledge hammer, rather than a fly swatter, to get rid of a fly,” says Elias.

The full study was published in the Journal of Clinical Investigation.