To find out why and how the effect lasts years after someone smokes their last cigarette, Duffy’s team turned to the DNA of their donors. Seemingly linked to everything from wildfire smoke to your parents’ trauma. epigenetic changesPhysical manipulation of the DNA molecule that turns genes on or off. Certainly, the long-term effect of smoking on the immune response is also linked to epigenetics.

Duffy admits that interpreting these effects can be tricky. It’s tempting to think of an overreactive immune system in smokers as “good”—when you’re injured or sick, short-term inflammation helps your body heal. But an exaggerated response that persists after the threat is gone can lead to chronic inflammation or autoimmune disease.

Quitting smoking brings the inflammatory response back to where it would have been without cigarettes, but the epigenetic changes associated with smoking may be difficult to reverse, suspects Sheena Cruickshank, an immunologist at the University of Manchester. Infected immune cells are long-lived, sticking around in the bloodstream for years. Ex-smokers may carry traces of past cigarettes with them until those cells die.

Of course, smoking behavior does not occur in a vacuum. All of the 1,000 donors in the study lead widely varied lives due to a rotating number of things beyond cigarettes. “We’re exposed to so many different things that it’s hard to tease them out,” says Adam Lacey-Hilbert, an immunologist at the Benaroya Research Institute in Seattle, Washington. The study adjusted for age and sex, but that certainly doesn’t account for everything. Cruickshank says that, while the effect of any individual environmental factor — smoking included — may be modest, these effects can stack on top of each other and lead to major changes in the immune system.

These findings may have important implications for vaccine delivery. We already make vaccine recommendations for certain age groups because inflammation (immunologists even have a term for this: “inflammation”) increases as we age. Lacey-Hilbert wonders if we should consider environmental factors such as people’s smoking habits (past and present) when planning the timing or formulation of their vaccinations. “Aging, like regular aging, just progresses—things get worse over time,” Lacy-Hilbert says. By contrast, he speculates, “you can imagine that smoking can add years to your immune lifespan.”

Duffy and colleagues Indoor environment plan Several follow-up projects are already underway to collect data from donors in Africa and Asia, as well as children and adults over 75 years of age. They are also preparing a 10-year follow-up report with a sample of 415 of the original 1,000 donors. The nature Study to see how their lifestyle changes during this decade affected their immune response. Going forward, Tsang hopes that future studies will conduct specific experiments to test some of these associations in the lab, so that How Our environment and behavior shape our immune system.

In the meantime, Cruickshank says, the best way to keep your immune system healthy is to follow the basic advice you’ve probably been told a thousand times: eat a varied, minimally processed diet. Move your body; Get enough rest and sleep. “In terms of being healthy, smoking is probably the worst thing you can do,” Duffy added.

Although we don’t yet know exactly how long smoking’s effect lasts, or whether it can be reversed, there is some good news: After quitting, smoking’s effect on the immune response appears to fade over time. Gives. “The best time to quit smoking is now,” says Duffy. “It’s always a good time.”